diff --git a/stint/io.nim b/stint/io.nim
index 3359324..d1f98cf 100644
--- a/stint/io.nim
+++ b/stint/io.nim
@@ -216,13 +216,16 @@ func skipPrefixes(current_idx: var int, str: string, radix: range[2..16]) {.inli
   doAssert current_idx == 0, "skipPrefixes only works for prefixes (position 0 and 1 of the string)"
   if str[0] == '0':
     if str[1] in {'x', 'X'}:
-      doAssert radix == 16, "Parsing mismatch, 0x prefix is only valid for a hexadecimal number (base 16)"
+      if radix != 16:
+        raise newException(ValueError,"Parsing mismatch, 0x prefix is only valid for a hexadecimal number (base 16)")
       current_idx = 2
     elif str[1] in {'o', 'O'}:
-      doAssert radix == 8, "Parsing mismatch, 0o prefix is only valid for an octal number (base 8)"
+      if radix != 8:
+        raise newException(ValueError, "Parsing mismatch, 0o prefix is only valid for an octal number (base 8)")
       current_idx = 2
     elif str[1] in {'b', 'B'}:
-      doAssert radix == 2, "Parsing mismatch, 0b prefix is only valid for a binary number (base 2)"
+      if radix != 2:
+        raise newException(ValueError, "Parsing mismatch, 0b prefix is only valid for a binary number (base 2)")
       current_idx = 2
 
 func nextNonBlank(current_idx: var int, s: string) {.inline.} =
diff --git a/tests/test_io.nim b/tests/test_io.nim
index 93daddb..48ca288 100644
--- a/tests/test_io.nim
+++ b/tests/test_io.nim
@@ -1197,6 +1197,12 @@ proc main() =
       else:
         echo "Next test skipped when Stint forces uint32 backend in test mode"
 
+    test "Parsing an unexpected 0x prefix for a decimal string is a CatchableError and not a defect":
+      let s = "0x123456"
+      
+      expect(ValueError):
+        let value = parse(s, StUint[256], 10)
+
   suite "Testing conversion functions: Hex, Bytes, Endianness using secp256k1 curve":
 
     let