diff --git a/zokrates_stdlib/stdlib/utils/casts/field_to_u16.zok b/zokrates_stdlib/stdlib/utils/casts/field_to_u16.zok
index 810208d6..8febe4b2 100644
--- a/zokrates_stdlib/stdlib/utils/casts/field_to_u16.zok
+++ b/zokrates_stdlib/stdlib/utils/casts/field_to_u16.zok
@@ -1,9 +1,7 @@
-from "EMBED" import unpack, u16_from_bits
+from "field" import FIELD_SIZE_IN_BITS
+import "utils/pack/bool/unpack"
+import "utils/casts/u16_from_bits"
 
-const field U16_MAX = 65535
-
-// Condition: field value is asserted to be in range [0, U16_MAX]
 def main(field input) -> u16:
-    assert(input <= U16_MAX)
-    bool[16] bits = unpack(input)
-    return u16_from_bits(bits)
\ No newline at end of file
+    bool[FIELD_SIZE_IN_BITS] bits = unpack(input)
+    return u16_from_bits(bits[FIELD_SIZE_IN_BITS-16..])
\ No newline at end of file
diff --git a/zokrates_stdlib/stdlib/utils/casts/field_to_u32.zok b/zokrates_stdlib/stdlib/utils/casts/field_to_u32.zok
index fc5c6a56..28577d79 100644
--- a/zokrates_stdlib/stdlib/utils/casts/field_to_u32.zok
+++ b/zokrates_stdlib/stdlib/utils/casts/field_to_u32.zok
@@ -1,9 +1,7 @@
-from "EMBED" import unpack, u32_from_bits
+from "field" import FIELD_SIZE_IN_BITS
+import "utils/pack/bool/unpack"
+import "utils/casts/u32_from_bits"
 
-const field U32_MAX = 4294967295
-
-// Condition: field value is asserted to be in range [0, U32_MAX]
 def main(field input) -> u32:
-    assert(input <= U32_MAX)
-    bool[32] bits = unpack(input)
-    return u32_from_bits(bits)
\ No newline at end of file
+    bool[FIELD_SIZE_IN_BITS] bits = unpack(input)
+    return u32_from_bits(bits[FIELD_SIZE_IN_BITS-32..])
\ No newline at end of file
diff --git a/zokrates_stdlib/stdlib/utils/casts/field_to_u64.zok b/zokrates_stdlib/stdlib/utils/casts/field_to_u64.zok
index 1b99ee74..d614ebcf 100644
--- a/zokrates_stdlib/stdlib/utils/casts/field_to_u64.zok
+++ b/zokrates_stdlib/stdlib/utils/casts/field_to_u64.zok
@@ -1,9 +1,7 @@
-from "EMBED" import unpack, u64_from_bits
+from "field" import FIELD_SIZE_IN_BITS
+import "utils/pack/bool/unpack"
+import "utils/casts/u64_from_bits"
 
-const field U64_MAX = 18446744073709551615
-
-// Condition: field value is asserted to be in range [0, U64_MAX]
 def main(field input) -> u64:
-    assert(input <= U64_MAX)
-    bool[64] bits = unpack(input)
-    return u64_from_bits(bits)
\ No newline at end of file
+    bool[FIELD_SIZE_IN_BITS] bits = unpack(input)
+    return u64_from_bits(bits[FIELD_SIZE_IN_BITS-64..])
\ No newline at end of file
diff --git a/zokrates_stdlib/stdlib/utils/casts/field_to_u8.zok b/zokrates_stdlib/stdlib/utils/casts/field_to_u8.zok
index bda7f6e2..99c795fd 100644
--- a/zokrates_stdlib/stdlib/utils/casts/field_to_u8.zok
+++ b/zokrates_stdlib/stdlib/utils/casts/field_to_u8.zok
@@ -1,9 +1,7 @@
-from "EMBED" import unpack, u8_from_bits
+from "field" import FIELD_SIZE_IN_BITS
+import "utils/pack/bool/unpack"
+import "utils/casts/u8_from_bits"
 
-const field U8_MAX = 255
-
-// Condition: field value is asserted to be in range [0, U8_MAX]
 def main(field input) -> u8:
-    assert(input <= U8_MAX)
-    bool[8] bits = unpack(input)
-    return u8_from_bits(bits)
\ No newline at end of file
+    bool[FIELD_SIZE_IN_BITS] bits = unpack(input)
+    return u8_from_bits(bits[FIELD_SIZE_IN_BITS-8..])
\ No newline at end of file
diff --git a/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.json b/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.json
index 1c988f73..0e617ee3 100644
--- a/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.json
+++ b/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.json
@@ -4,11 +4,11 @@
     "tests": [
         {
             "input": {
-                "values": ["0", "1", "18446744073709551615", "42", "0", "1", "4294967295", "42", "0", "1", "65535", "42", "0", "1", "255", "42"]
+                "values": ["0", "1", "18446744073709551615", "18446744073709551616", "18446744073709551658", "0", "1", "4294967295", "4294967296", "4294967338", "0", "1", "65535", "65536", "65578", "0", "1", "255", "256", "298"]
             },
             "output": {
                 "Ok": {
-                    "values": ["0", "1", "18446744073709551615", "42", "0", "1", "4294967295", "42", "0", "1", "65535", "42", "0", "1", "255", "42"]
+                    "values": ["0", "1", "18446744073709551615", "0", "42", "0", "1", "4294967295", "0", "42", "0", "1", "65535", "0", "42", "0", "1", "255", "0", "42"]
                 }
             }
         }
diff --git a/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.zok b/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.zok
index b8a3de76..4d5be3bb 100644
--- a/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.zok
+++ b/zokrates_stdlib/tests/tests/utils/casts/field_to_uint.zok
@@ -3,13 +3,13 @@ import "utils/casts/field_to_u32"
 import "utils/casts/field_to_u16"
 import "utils/casts/field_to_u8"
 
-def main(field[4] a, field[4] b, field[4] c, field[4] d) -> (u64[4], u32[4], u16[4], u8[4]):
-    u64[4] e = [0; 4]
-    u32[4] f = [0; 4]
-    u16[4] g = [0; 4]
-    u8[4] h = [0; 4]
+def main(field[5] a, field[5] b, field[5] c, field[5] d) -> (u64[5], u32[5], u16[5], u8[5]):
+    u64[5] e = [0; 5]
+    u32[5] f = [0; 5]
+    u16[5] g = [0; 5]
+    u8[5] h = [0; 5]
 
-    for u32 i in 0..4 do
+    for u32 i in 0..5 do
         e[i] = field_to_u64(a[i])
         f[i] = field_to_u32(b[i])
         g[i] = field_to_u16(c[i])