diff --git a/src/ecsignature.js b/src/ecsignature.js
index cbf9f81..151e962 100644
--- a/src/ecsignature.js
+++ b/src/ecsignature.js
@@ -71,7 +71,7 @@ ECSignature.parseScriptSignature = function (buffer) {
   var hashType = buffer.readUInt8(buffer.length - 1)
   var hashTypeMod = hashType & ~0x80
 
-  assert(hashTypeMod > 0x00 && hashTypeMod < 0x04, 'Invalid hashType ' + hashType)
+  if (hashTypeMod <= 0x00 || hashTypeMod >= 0x04) throw new Error('Invalid hashType ' + hashType)
 
   return {
     signature: ECSignature.fromDER(buffer.slice(0, -1)),