diff --git a/zokrates_analysis/src/assembly_transformer.rs b/zokrates_analysis/src/assembly_transformer.rs
index eb4b8ef5..3d1e9567 100644
--- a/zokrates_analysis/src/assembly_transformer.rs
+++ b/zokrates_analysis/src/assembly_transformer.rs
@@ -1,3 +1,7 @@
+// A static analyser pass to transform user-defined constraints to the form `lin_comb === quad_comb`
+// This pass can fail if a non-quadratic constraint is found which cannot be transformed to the expected form
+
+use crate::ZirPropagator;
 use std::fmt;
 use zokrates_ast::zir::lqc::LinQuadComb;
 use zokrates_ast::zir::result_folder::{fold_field_expression, ResultFolder};
@@ -17,8 +21,7 @@ pub struct AssemblyTransformer;
 
 impl AssemblyTransformer {
     pub fn transform<T: Field>(p: ZirProgram<T>) -> Result<ZirProgram<T>, Error> {
-        let mut f = AssemblyTransformer;
-        f.fold_program(p)
+        AssemblyTransformer.fold_program(p)
     }
 }
 
@@ -52,7 +55,7 @@ impl<'ast, T: Field> ResultFolder<'ast, T> for AssemblyTransformer {
                 match is_quadratic {
                     true => Ok(ZirAssemblyStatement::Constraint(lhs, rhs)),
                     false => {
-                        let sub = FieldElementExpression::Sub(box lhs.clone(), box rhs.clone());
+                        let sub = FieldElementExpression::Sub(box lhs, box rhs);
                         let mut lqc = LinQuadComb::try_from(sub.clone()).map_err(|_| {
                             Error("Non-quadratic constraints are not allowed".to_string())
                         })?;
@@ -60,72 +63,72 @@ impl<'ast, T: Field> ResultFolder<'ast, T> for AssemblyTransformer {
                         let linear = lqc
                             .linear
                             .into_iter()
-                            .filter_map(|(c, i)| match c {
-                                c if c == T::from(0) => None,
-                                c if c == T::from(1) => Some(FieldElementExpression::identifier(i)),
-                                _ => Some(FieldElementExpression::Mult(
+                            .map(|(c, i)| {
+                                FieldElementExpression::Mult(
                                     box FieldElementExpression::Number(c),
                                     box FieldElementExpression::identifier(i),
-                                )),
+                                )
                             })
-                            .reduce(|p, n| FieldElementExpression::Add(box p, box n))
-                            .unwrap_or_else(|| FieldElementExpression::Number(T::from(0)));
+                            .fold(FieldElementExpression::Number(T::from(0)), |acc, e| {
+                                FieldElementExpression::Add(box acc, box e)
+                            });
 
-                        let lhs = match lqc.constant {
-                            c if c == T::from(0) => linear,
-                            c => FieldElementExpression::Add(
-                                box FieldElementExpression::Number(c),
-                                box linear,
-                            ),
-                        };
+                        let lhs = FieldElementExpression::Add(
+                            box FieldElementExpression::Number(lqc.constant),
+                            box linear,
+                        );
 
                         let rhs: FieldElementExpression<'ast, T> = if lqc.quadratic.len() > 1 {
-                            let is_common_factor = |id: &Identifier<'ast>,
-                                                    q: &Vec<(
-                                T,
-                                Identifier<'ast>,
-                                Identifier<'ast>,
-                            )>| {
-                                q.iter().all(|(_, i0, i1)| i0.eq(id) || i1.eq(id))
-                            };
+                            let common_factors = lqc.quadratic.iter().fold(
+                                None,
+                                |acc: Option<Vec<Identifier>>, (_, a, b)| {
+                                    Some(
+                                        acc.map(|factors| {
+                                            factors
+                                                .into_iter()
+                                                .filter(|f| f == a || f == b)
+                                                .collect()
+                                        })
+                                        .unwrap_or_else(|| vec![a.clone(), b.clone()]),
+                                    )
+                                },
+                            );
 
-                            let common_factor: Option<Identifier<'ast>> =
-                                lqc.quadratic.iter().find_map(|(_, i0, i1)| {
-                                    if is_common_factor(i0, &lqc.quadratic) {
-                                        Some(i0.clone())
-                                    } else if is_common_factor(i1, &lqc.quadratic) {
-                                        Some(i1.clone())
-                                    } else {
-                                        None
-                                    }
-                                });
-
-                            match common_factor {
-                                Some(id) => Ok(FieldElementExpression::Mult(
+                            match common_factors {
+                                Some(factors) => Ok(FieldElementExpression::Mult(
                                     box lqc
                                         .quadratic
                                         .into_iter()
-                                        .filter_map(|(c, i0, i1)| {
+                                        .map(|(c, i0, i1)| {
                                             let c = T::zero() - c;
-                                            let id = if id.eq(&i0) { i1 } else { i0 };
-                                            match c {
-                                                c if c == T::from(0) => None,
-                                                c if c == T::from(1) => {
-                                                    Some(FieldElementExpression::identifier(id))
-                                                }
-                                                _ => Some(FieldElementExpression::Mult(
-                                                    box FieldElementExpression::Number(c),
-                                                    box FieldElementExpression::identifier(id),
-                                                )),
-                                            }
+                                            let i0 = match factors.contains(&i0) {
+                                                true => FieldElementExpression::Number(T::from(1)),
+                                                false => FieldElementExpression::identifier(i0),
+                                            };
+                                            let i1 = match factors.contains(&i1) {
+                                                true => FieldElementExpression::Number(T::from(1)),
+                                                false => FieldElementExpression::identifier(i1),
+                                            };
+                                            FieldElementExpression::Mult(
+                                                box FieldElementExpression::Number(c),
+                                                box FieldElementExpression::Mult(box i0, box i1),
+                                            )
                                         })
-                                        .reduce(|p, n| FieldElementExpression::Add(box p, box n))
-                                        .unwrap_or_else(|| {
-                                            FieldElementExpression::Number(T::from(0))
-                                        }),
-                                    box FieldElementExpression::identifier(id),
+                                        .fold(
+                                            FieldElementExpression::Number(T::from(0)),
+                                            |acc, e| FieldElementExpression::Add(box acc, box e),
+                                        ),
+                                    box factors.into_iter().fold(
+                                        FieldElementExpression::Number(T::from(1)),
+                                        |acc, id| {
+                                            FieldElementExpression::Mult(
+                                                box acc,
+                                                box FieldElementExpression::identifier(id),
+                                            )
+                                        },
+                                    ),
                                 )),
-                                _ => Err(Error(
+                                None => Err(Error(
                                     "Non-quadratic constraints are not allowed".to_string(),
                                 )),
                             }?
@@ -144,6 +147,15 @@ impl<'ast, T: Field> ResultFolder<'ast, T> for AssemblyTransformer {
                                 .unwrap_or_else(|| FieldElementExpression::Number(T::from(0)))
                         };
 
+                        let mut propagator = ZirPropagator::default();
+                        let lhs = propagator
+                            .fold_field_expression(lhs)
+                            .map_err(|e| Error(e.to_string()))?;
+
+                        let rhs = propagator
+                            .fold_field_expression(rhs)
+                            .map_err(|e| Error(e.to_string()))?;
+
                         Ok(ZirAssemblyStatement::Constraint(lhs, rhs))
                     }
                 }
diff --git a/zokrates_analysis/src/flatten_complex_types.rs b/zokrates_analysis/src/flatten_complex_types.rs
index 2d17575e..56bb55c9 100644
--- a/zokrates_analysis/src/flatten_complex_types.rs
+++ b/zokrates_analysis/src/flatten_complex_types.rs
@@ -458,6 +458,27 @@ impl<'ast, T: Field> Flattener<T> {
     }
 }
 
+// This finder looks for identifiers that were not defined in some block of statements
+// These identifiers are used as function arguments when moving witness assignment expression
+// to a zir function.
+//
+// Example:
+// def main(field a, field mut b) -> field {
+//     asm {
+//         b <== a * a;
+//     }
+//     return b;
+// }
+// is turned into
+// def main(field a, field mut b) -> field {
+//     asm {
+//         b <-- (field a) -> field {
+//             return a * a;
+//         }
+//         b == a * a;
+//     }
+//     return b;
+// }
 #[derive(Default)]
 pub struct ArgumentFinder<'ast, T> {
     pub identifiers: HashMap<zir::Identifier<'ast>, zir::Type>,
diff --git a/zokrates_analysis/src/propagation.rs b/zokrates_analysis/src/propagation.rs
index a1c1764f..e8022ed6 100644
--- a/zokrates_analysis/src/propagation.rs
+++ b/zokrates_analysis/src/propagation.rs
@@ -12,7 +12,7 @@ use num_bigint::BigUint;
 use std::collections::HashMap;
 use std::convert::{TryFrom, TryInto};
 use std::fmt;
-use std::ops::{BitAnd, BitOr, BitXor, Mul, Shr, Sub};
+use std::ops::{BitAnd, BitOr, BitXor, Shl, Shr, Sub};
 use zokrates_ast::common::FlatEmbed;
 use zokrates_ast::typed::result_folder::*;
 use zokrates_ast::typed::types::Type;
@@ -402,7 +402,6 @@ impl<'ast, 'a, T: Field> ResultFolder<'ast, T> for Propagator<'ast, 'a, T> {
                     true => {
                         let r: Option<TypedExpression<'ast, T>> = match embed_call.embed {
                             FlatEmbed::FieldToBoolUnsafe => Ok(None), // todo
-                            FlatEmbed::BoolToField => Ok(None),       // todo
                             FlatEmbed::BitArrayLe => Ok(None),        // todo
                             FlatEmbed::U64FromBits => Ok(Some(process_u_from_bits(
                                 &embed_call.arguments,
@@ -874,6 +873,12 @@ impl<'ast, 'a, T: Field> ResultFolder<'ast, T> for Propagator<'ast, 'a, T> {
                             T::try_from(n1.to_biguint().bitxor(n2.to_biguint())).unwrap(),
                         ))
                     }
+                    (FieldElementExpression::Number(n), e)
+                    | (e, FieldElementExpression::Number(n))
+                        if n == T::from(0) =>
+                    {
+                        Ok(e)
+                    }
                     (e1, e2) if e1.eq(&e2) => Ok(FieldElementExpression::Number(T::from(0))),
                     (e1, e2) => Ok(FieldElementExpression::Xor(box e1, box e2)),
                 }
@@ -948,8 +953,7 @@ impl<'ast, 'a, T: Field> ResultFolder<'ast, T> for Propagator<'ast, 'a, T> {
                         let mask: BigUint = two.pow(T::get_required_bits()).sub(1usize);
 
                         Ok(FieldElementExpression::Number(
-                            T::try_from(n.to_biguint().mul(two.pow(by as usize)).bitand(mask))
-                                .unwrap(),
+                            T::try_from(n.to_biguint().shl(by as usize).bitand(mask)).unwrap(),
                         ))
                     }
                     (e, by) => Ok(FieldElementExpression::LeftShift(box e, box by)),
diff --git a/zokrates_analysis/src/zir_propagation.rs b/zokrates_analysis/src/zir_propagation.rs
index 1a026b17..298166bf 100644
--- a/zokrates_analysis/src/zir_propagation.rs
+++ b/zokrates_analysis/src/zir_propagation.rs
@@ -2,7 +2,7 @@ use num::traits::Pow;
 use num_bigint::BigUint;
 use std::collections::HashMap;
 use std::fmt;
-use std::ops::{BitAnd, BitOr, BitXor, Mul, Shr, Sub};
+use std::ops::{BitAnd, BitOr, BitXor, Shl, Shr, Sub};
 use zokrates_ast::zir::types::UBitwidth;
 use zokrates_ast::zir::{
     result_folder::*, Conditional, ConditionalExpression, ConditionalOrExpression, Expr, Id,
@@ -334,8 +334,7 @@ impl<'ast, T: Field> ResultFolder<'ast, T> for ZirPropagator<'ast, T> {
                         let mask: BigUint = two.pow(T::get_required_bits()).sub(1usize);
 
                         Ok(FieldElementExpression::Number(
-                            T::try_from(n.to_biguint().mul(two.pow(by as usize)).bitand(mask))
-                                .unwrap(),
+                            T::try_from(n.to_biguint().shl(by as usize).bitand(mask)).unwrap(),
                         ))
                     }
                     (e, by) => Ok(FieldElementExpression::LeftShift(box e, box by)),
diff --git a/zokrates_ast/src/common/embed.rs b/zokrates_ast/src/common/embed.rs
index 3f961cd9..58294142 100644
--- a/zokrates_ast/src/common/embed.rs
+++ b/zokrates_ast/src/common/embed.rs
@@ -32,7 +32,6 @@ cfg_if::cfg_if! {
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Copy, PartialOrd, Ord, Serialize, Deserialize)]
 pub enum FlatEmbed {
     FieldToBoolUnsafe,
-    BoolToField,
     BitArrayLe,
     Unpack,
     U8ToBits,
@@ -55,9 +54,6 @@ impl FlatEmbed {
             FlatEmbed::FieldToBoolUnsafe => UnresolvedSignature::new()
                 .inputs(vec![UnresolvedType::FieldElement.into()])
                 .output(UnresolvedType::Boolean.into()),
-            FlatEmbed::BoolToField => UnresolvedSignature::new()
-                .inputs(vec![UnresolvedType::Boolean.into()])
-                .output(UnresolvedType::FieldElement.into()),
             FlatEmbed::BitArrayLe => UnresolvedSignature::new()
                 .generics(vec![ConstantGenericNode::mock("N")])
                 .inputs(vec![
@@ -197,9 +193,6 @@ impl FlatEmbed {
             FlatEmbed::FieldToBoolUnsafe => DeclarationSignature::new()
                 .inputs(vec![DeclarationType::FieldElement])
                 .output(DeclarationType::Boolean),
-            FlatEmbed::BoolToField => DeclarationSignature::new()
-                .inputs(vec![DeclarationType::Boolean])
-                .output(DeclarationType::FieldElement),
             FlatEmbed::BitArrayLe => DeclarationSignature::new()
                 .generics(vec![Some(DeclarationConstant::Generic(
                     GenericIdentifier::with_name("N").with_index(0),
@@ -307,7 +300,6 @@ impl FlatEmbed {
     pub fn id(&self) -> &'static str {
         match self {
             FlatEmbed::FieldToBoolUnsafe => "_FIELD_TO_BOOL_UNSAFE",
-            FlatEmbed::BoolToField => "_BOOL_TO_FIELD",
             FlatEmbed::BitArrayLe => "_BIT_ARRAY_LT",
             FlatEmbed::Unpack => "_UNPACK",
             FlatEmbed::U8ToBits => "_U8_TO_BITS",
diff --git a/zokrates_ast/src/common/error.rs b/zokrates_ast/src/common/error.rs
index 28c209f4..499ac97d 100644
--- a/zokrates_ast/src/common/error.rs
+++ b/zokrates_ast/src/common/error.rs
@@ -3,7 +3,7 @@ use std::fmt;
 
 #[derive(Debug, Clone, Serialize, Deserialize, Hash, PartialEq, Eq)]
 pub enum RuntimeError {
-    UserConstraint,
+    SourceAssemblyConstraint,
     BellmanConstraint,
     BellmanOneBinding,
     BellmanInputBinding,
@@ -50,7 +50,7 @@ impl RuntimeError {
 
         !matches!(
             self,
-            UserConstraint
+            SourceAssemblyConstraint
                 | SourceAssertion(_)
                 | Inverse
                 | SelectRangeCheck
@@ -65,7 +65,7 @@ impl fmt::Display for RuntimeError {
         use RuntimeError::*;
 
         let msg = match self {
-            UserConstraint => "User constraint is unsatisfied",
+            SourceAssemblyConstraint => "Source constraint is unsatisfied",
             BellmanConstraint => "Bellman constraint is unsatisfied",
             BellmanOneBinding => "Bellman ~one binding is unsatisfied",
             BellmanInputBinding => "Bellman input binding is unsatisfied",
diff --git a/zokrates_ast/src/common/solvers.rs b/zokrates_ast/src/common/solvers.rs
index 26247f59..915d9ceb 100644
--- a/zokrates_ast/src/common/solvers.rs
+++ b/zokrates_ast/src/common/solvers.rs
@@ -20,7 +20,7 @@ pub enum Solver<'ast, T> {
     SnarkVerifyBls12377(usize),
 }
 
-impl<'ast, T: fmt::Debug + fmt::Display> fmt::Display for Solver<'ast, T> {
+impl<'ast, T: fmt::Debug> fmt::Display for Solver<'ast, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             Solver::Zir(_) => write!(f, "Zir(..)"),
diff --git a/zokrates_ast/src/zir/lqc.rs b/zokrates_ast/src/zir/lqc.rs
index 746bdc31..98b1c30e 100644
--- a/zokrates_ast/src/zir/lqc.rs
+++ b/zokrates_ast/src/zir/lqc.rs
@@ -1,14 +1,17 @@
 use crate::zir::{FieldElementExpression, Identifier};
 use zokrates_field::Field;
 
+pub type LinearTerm<'ast, T> = (T, Identifier<'ast>);
+pub type QuadraticTerm<'ast, T> = (T, Identifier<'ast>, Identifier<'ast>);
+
 #[derive(Clone, PartialEq, Hash, Eq, Debug, Default)]
 pub struct LinQuadComb<'ast, T> {
     // the constant terms
     pub constant: T,
     // the linear terms
-    pub linear: Vec<(T, Identifier<'ast>)>,
+    pub linear: Vec<LinearTerm<'ast, T>>,
     // the quadratic terms
-    pub quadratic: Vec<(T, Identifier<'ast>, Identifier<'ast>)>,
+    pub quadratic: Vec<QuadraticTerm<'ast, T>>,
 }
 
 impl<'ast, T: Field> std::ops::Add for LinQuadComb<'ast, T> {
diff --git a/zokrates_ast/src/zir/mod.rs b/zokrates_ast/src/zir/mod.rs
index b793e4d6..ba7a0e3e 100644
--- a/zokrates_ast/src/zir/mod.rs
+++ b/zokrates_ast/src/zir/mod.rs
@@ -166,7 +166,8 @@ pub enum ZirStatement<'ast, T> {
         FormatString,
         Vec<(ConcreteType, Vec<ZirExpression<'ast, T>>)>,
     ),
-    Assembly(#[serde(borrow)] Vec<ZirAssemblyStatement<'ast, T>>),
+    #[serde(borrow)]
+    Assembly(Vec<ZirAssemblyStatement<'ast, T>>),
 }
 
 impl<'ast, T: fmt::Display> fmt::Display for ZirStatement<'ast, T> {
diff --git a/zokrates_cli/examples/book/assembly/bool_to_field.zok b/zokrates_cli/examples/book/assembly/bool_to_field.zok
index 4c1284b0..48f0e017 100644
--- a/zokrates_cli/examples/book/assembly/bool_to_field.zok
+++ b/zokrates_cli/examples/book/assembly/bool_to_field.zok
@@ -1,8 +1,6 @@
-from "EMBED" import bool_to_field;
-
 def main(bool x) -> field {
     // `x` is constrained by the compiler automatically so we can safely
-    //  treat it as `field` with no extra cost
-    field out = bool_to_field(x);
+    //  convert to `field` with no extra cost
+    field out = x ? 1 : 0;
     return out;
 }
\ No newline at end of file
diff --git a/zokrates_cli/examples/book/assembly/division.zok b/zokrates_cli/examples/book/assembly/division.zok
index c38e18ee..b9f65af2 100644
--- a/zokrates_cli/examples/book/assembly/division.zok
+++ b/zokrates_cli/examples/book/assembly/division.zok
@@ -1,7 +1,11 @@
-def main(field a, field b) {
+def main(field a, field b) -> field {
     field mut c = 0;
+    field mut invb = 0;
     asm {
-        c <-- a / b;
+        invb <-- b == 0 ? 0 : 1 / b;
+        invb * b === 1;
+        c <-- invb * a;
         a === b * c;
     }
+    return c;
 }
\ No newline at end of file
diff --git a/zokrates_cli/examples/book/assembly/field_to_bool.zok b/zokrates_cli/examples/book/assembly/field_to_bool.zok
index b213b346..2e9f0552 100644
--- a/zokrates_cli/examples/book/assembly/field_to_bool.zok
+++ b/zokrates_cli/examples/book/assembly/field_to_bool.zok
@@ -5,7 +5,8 @@ def main(field x) -> bool {
     asm {
         x * (x - 1) === 0;
     }
-    // we can treat `x` as `bool` afterwards, as we constrained it properly
+    // we can convert `x` to `bool` afterwards, as we constrained it properly
+    // if we failed to constrain `x` to `0` or `1`, the call to `field_to_bool_unsafe` introduces undefined behavior
     // `field_to_bool_unsafe` call does not produce any extra constraints
     bool out = field_to_bool_unsafe(x);
     return out;
diff --git a/zokrates_cli/src/bin.rs b/zokrates_cli/src/bin.rs
index a2b857a9..a5f8a31f 100644
--- a/zokrates_cli/src/bin.rs
+++ b/zokrates_cli/src/bin.rs
@@ -259,7 +259,7 @@ mod tests {
 
             let interpreter = zokrates_interpreter::Interpreter::default();
 
-            let res = interpreter.execute(artifacts.prog(), &[Bn128Field::from(0u32)]);
+            let res = interpreter.execute(artifacts.prog(), &[Bn128Field::from(0)]);
 
             assert!(res.is_err());
         }
diff --git a/zokrates_codegen/src/lib.rs b/zokrates_codegen/src/lib.rs
index 25317391..ba3b92da 100644
--- a/zokrates_codegen/src/lib.rs
+++ b/zokrates_codegen/src/lib.rs
@@ -1050,7 +1050,6 @@ impl<'ast, T: Field> Flattener<'ast, T> {
 
         match embed {
             FlatEmbed::FieldToBoolUnsafe => vec![params.pop().unwrap()],
-            FlatEmbed::BoolToField => vec![params.pop().unwrap()],
             FlatEmbed::U8ToBits => self.u_to_bits(params.pop().unwrap(), 8.into()),
             FlatEmbed::U16ToBits => self.u_to_bits(params.pop().unwrap(), 16.into()),
             FlatEmbed::U32ToBits => self.u_to_bits(params.pop().unwrap(), 32.into()),
@@ -2255,7 +2254,7 @@ impl<'ast, T: Field> Flattener<'ast, T> {
                 statements_flattened.push_back(FlatStatement::Condition(
                     lhs,
                     rhs,
-                    RuntimeError::UserConstraint,
+                    RuntimeError::SourceAssemblyConstraint,
                 ));
             }
         }
diff --git a/zokrates_core/src/imports.rs b/zokrates_core/src/imports.rs
index 4bdf4940..f7fa95f1 100644
--- a/zokrates_core/src/imports.rs
+++ b/zokrates_core/src/imports.rs
@@ -151,10 +151,6 @@ impl Importer {
                     id: symbol.get_alias(),
                     symbol: Symbol::Flat(FlatEmbed::FieldToBoolUnsafe),
                 },
-                "bool_to_field" => SymbolDeclaration {
-                    id: symbol.get_alias(),
-                    symbol: Symbol::Flat(FlatEmbed::BoolToField),
-                },
                 "bit_array_le" => SymbolDeclaration {
                     id: symbol.get_alias(),
                     symbol: Symbol::Flat(FlatEmbed::BitArrayLe),
diff --git a/zokrates_core/src/semantics.rs b/zokrates_core/src/semantics.rs
index b1ef9286..70bde599 100644
--- a/zokrates_core/src/semantics.rs
+++ b/zokrates_core/src/semantics.rs
@@ -1804,10 +1804,9 @@ impl<'ast, T: Field> Checker<'ast, T> {
                 let e = match checked_e {
                     TypedExpression::FieldElement(e) => Ok(e),
                     TypedExpression::Int(e) => Ok(FieldElementExpression::try_from_int(e).unwrap()),
-                    _ => Err(ErrorInner {
+                    e => Err(ErrorInner {
                         pos: Some(pos),
-                        message: "Only field element expressions are allowed in the assembly block"
-                            .to_string(),
+                        message: format!("The right hand side of an assembly assignment must be of type field, found {}", e.get_type())
                     }),
                 }?;
 
@@ -1819,9 +1818,9 @@ impl<'ast, T: Field> Checker<'ast, T> {
                                 TypedAssemblyStatement::Assignment(assignee.clone(), e.clone()),
                                 TypedAssemblyStatement::Constraint(assignee.into(), e),
                             ]),
-                            _ => Err(ErrorInner {
+                            ty => Err(ErrorInner {
                                 pos: Some(pos),
-                                message: "Assignee must be of type `field`".to_string(),
+                                message: format!("Assignee must be of type field, found {}", ty),
                             }),
                         }
                     }
@@ -1849,10 +1848,13 @@ impl<'ast, T: Field> Checker<'ast, T> {
                         FieldElementExpression::try_from_int(lhs).unwrap(),
                         FieldElementExpression::try_from_int(rhs).unwrap(),
                     )),
-                    _ => Err(ErrorInner {
+                    (e1, e2) => Err(ErrorInner {
                         pos: Some(pos),
-                        message: "Only field element expressions are allowed in the assembly block"
-                            .to_string(),
+                        message: format!(
+                            "Assembly constraint expected expressions of type field, found {}, {}",
+                            e1.get_type(),
+                            e2.get_type()
+                        ),
                     }),
                 }?;
 
@@ -1873,14 +1875,12 @@ impl<'ast, T: Field> Checker<'ast, T> {
             Statement::Assembly(statements) => {
                 let mut checked_statements = vec![];
                 for s in statements {
-                    checked_statements.push(
+                    checked_statements.extend(
                         self.check_assembly_statement(s, module_id, types)
                             .map_err(|e| vec![e])?,
                     );
                 }
-                Ok(TypedStatement::Assembly(
-                    checked_statements.into_iter().flatten().collect(),
-                ))
+                Ok(TypedStatement::Assembly(checked_statements))
             }
             Statement::Log(l, expressions) => {
                 let l = FormatString::from(l);
diff --git a/zokrates_core_test/tests/tests/assembly/binary_check.json b/zokrates_core_test/tests/tests/assembly/binary_check.json
index 53912338..0973db36 100644
--- a/zokrates_core_test/tests/tests/assembly/binary_check.json
+++ b/zokrates_core_test/tests/tests/assembly/binary_check.json
@@ -29,7 +29,7 @@
       "output": {
         "Err": {
           "UnsatisfiedConstraint": {
-            "error": "UserConstraint"
+            "error": "SourceAssemblyConstraint"
           }
         }
       }
diff --git a/zokrates_core_test/tests/tests/assembly/bitify.json b/zokrates_core_test/tests/tests/assembly/bitify.json
index ba04a1e6..19beb2bd 100644
--- a/zokrates_core_test/tests/tests/assembly/bitify.json
+++ b/zokrates_core_test/tests/tests/assembly/bitify.json
@@ -48,7 +48,7 @@
       "output": {
         "Err": {
           "UnsatisfiedConstraint": {
-            "error": "UserConstraint"
+            "error": "SourceAssemblyConstraint"
           }
         }
       }
diff --git a/zokrates_core_test/tests/tests/assembly/division.json b/zokrates_core_test/tests/tests/assembly/division.json
index 7478326f..9e3e511a 100644
--- a/zokrates_core_test/tests/tests/assembly/division.json
+++ b/zokrates_core_test/tests/tests/assembly/division.json
@@ -1,6 +1,6 @@
 {
   "curves": ["Bn128"],
-  "max_constraint_count": 2,
+  "max_constraint_count": 3,
   "tests": [
     {
       "input": {
@@ -14,11 +14,13 @@
     },
     {
       "input": {
-        "values": ["4", "0"]
+        "values": ["0", "0"]
       },
       "output": {
         "Err": {
-          "Solver": "Assertion failed: `Division by zero`"
+          "UnsatisfiedConstraint": {
+            "error": "SourceAssemblyConstraint"
+          }
         }
       }
     }
diff --git a/zokrates_core_test/tests/tests/assembly/division.zok b/zokrates_core_test/tests/tests/assembly/division.zok
index 35669ffd..b9f65af2 100644
--- a/zokrates_core_test/tests/tests/assembly/division.zok
+++ b/zokrates_core_test/tests/tests/assembly/division.zok
@@ -1,8 +1,11 @@
-def main(field x, field y) -> field {
-    field mut z = 0;
+def main(field a, field b) -> field {
+    field mut c = 0;
+    field mut invb = 0;
     asm {
-        z <-- x / y;
-        z * y === x;
+        invb <-- b == 0 ? 0 : 1 / b;
+        invb * b === 1;
+        c <-- invb * a;
+        a === b * c;
     }
-    return z;
+    return c;
 }
\ No newline at end of file
diff --git a/zokrates_core_test/tests/tests/embed/bool_to_field.json b/zokrates_core_test/tests/tests/embed/bool_to_field.json
deleted file mode 100644
index 5e78b298..00000000
--- a/zokrates_core_test/tests/tests/embed/bool_to_field.json
+++ /dev/null
@@ -1,26 +0,0 @@
-{
-  "curves": ["Bn128"],
-  "max_constraint_count": 2,
-  "tests": [
-    {
-      "input": {
-        "values": [false]
-      },
-      "output": {
-        "Ok": {
-          "value": "0"
-        }
-      }
-    },
-    {
-      "input": {
-        "values": [true]
-      },
-      "output": {
-        "Ok": {
-          "value": "1"
-        }
-      }
-    }
-  ]
-}
diff --git a/zokrates_core_test/tests/tests/embed/bool_to_field.zok b/zokrates_core_test/tests/tests/embed/bool_to_field.zok
deleted file mode 100644
index 457ac06d..00000000
--- a/zokrates_core_test/tests/tests/embed/bool_to_field.zok
+++ /dev/null
@@ -1,6 +0,0 @@
-from "EMBED" import bool_to_field;
-
-def main(bool x) -> field {
-    field out = bool_to_field(x);
-    return out;
-}
\ No newline at end of file
diff --git a/zokrates_core_test/tests/tests/embed/field_to_bool.json b/zokrates_core_test/tests/tests/embed/field_to_bool.json
index d24af7e0..b8357755 100644
--- a/zokrates_core_test/tests/tests/embed/field_to_bool.json
+++ b/zokrates_core_test/tests/tests/embed/field_to_bool.json
@@ -29,7 +29,7 @@
       "output": {
         "Err": {
           "UnsatisfiedConstraint": {
-            "error": "UserConstraint"
+            "error": "SourceAssemblyConstraint"
           }
         }
       }
diff --git a/zokrates_test/tests/out_of_range.rs b/zokrates_test/tests/out_of_range.rs
index 781bae76..ea280025 100644
--- a/zokrates_test/tests/out_of_range.rs
+++ b/zokrates_test/tests/out_of_range.rs
@@ -42,7 +42,7 @@ fn lt_field() {
     assert!(interpreter
         .execute(
             res.prog(),
-            &[Bn128Field::from(10000u32), Bn128Field::from(5555u32)]
+            &[Bn128Field::from(10000), Bn128Field::from(5555)]
         )
         .is_err());
 }
@@ -78,7 +78,7 @@ fn lt_uint() {
     assert!(interpreter
         .execute(
             res.prog(),
-            &[Bn128Field::from(10000u32), Bn128Field::from(5555u32)]
+            &[Bn128Field::from(10000), Bn128Field::from(5555)]
         )
         .is_err());
 }
@@ -123,7 +123,7 @@ fn unpack256() {
     let interpreter = Interpreter::try_out_of_range();
 
     assert!(interpreter
-        .execute(res.prog(), &[Bn128Field::from(0u32)])
+        .execute(res.prog(), &[Bn128Field::from(0)])
         .is_err());
 }
 
@@ -167,6 +167,6 @@ fn unpack256_unchecked() {
     let interpreter = Interpreter::try_out_of_range();
 
     assert!(interpreter
-        .execute(res.prog(), &[Bn128Field::from(0u32)])
+        .execute(res.prog(), &[Bn128Field::from(0)])
         .is_ok());
 }