diff --git a/src/absy.rs b/src/absy.rs
index 4b9bddc1..b2732fc0 100644
--- a/src/absy.rs
+++ b/src/absy.rs
@@ -93,9 +93,14 @@ impl Expression {
                     if var.contains("_b") {
                         let var_name = var.split("_b").collect::<Vec<_>>()[0];
                         let mut num = inputs[var_name];
-                        assert!(num >= 0, format!("num < 0: {}", num));
-                        // TODO support negative numbers with two's complement!?
-                        for i in (0..8).rev() {
+                        let bits = 8;
+                        if num < 0 {
+                            num += 2i32.pow(bits - 1);
+                            inputs.insert(format!("{}_b{}", &var_name, bits - 1), 1);
+                        } else {
+                            inputs.insert(format!("{}_b{}", &var_name, bits - 1), 0);
+                        }
+                        for i in (0..bits - 1).rev() {
                             if 2i32.pow(i) <= num {
                                 num -= 2i32.pow(i);
                                 inputs.insert(format!("{}_b{}", &var_name, i), 1);
diff --git a/src/flatten.rs b/src/flatten.rs
index 1600f620..e19978bb 100644
--- a/src/flatten.rs
+++ b/src/flatten.rs
@@ -35,7 +35,7 @@ fn flatten_condition(statements_flattened: &mut Vec<Statement>, num_variables: &
                 ));
             }
             let mut expr = VariableReference(format!("{}_b0", &cond_result)); // * 2^0
-            for i in 1..bits {
+            for i in 1..bits - 1 {
                 expr = Add(
                     box Mult(
                         box VariableReference(format!("{}_b{}", &cond_result, i)),
@@ -44,6 +44,13 @@ fn flatten_condition(statements_flattened: &mut Vec<Statement>, num_variables: &
                     box expr
                 );
             }
+            expr = Add(
+                box Mult(
+                    box VariableReference(format!("{}_b{}", &cond_result, bits - 1)),
+                    box NumberLiteral(-2i32.pow(bits - 1))
+                ),
+                box expr
+            );
             statements_flattened.push(Statement::Definition(cond_result.to_string(), expr));
 
             let cond_true = format!("{}_b{}", &cond_result, bits - 1);