diff --git a/src/bigint.js b/src/bigint.js
index b2c594c..54bfac8 100644
--- a/src/bigint.js
+++ b/src/bigint.js
@@ -226,6 +226,11 @@ if (typeof(BigInt) != "undefined") {
         return this != b;
     };
 
+    wBigInt.prototype.toJSNumber = function() {
+        return Number(this);
+    };
+
+
 } else {
 
     var oldProto = bigInt.prototype;
diff --git a/src/calculateWitness.js b/src/calculateWitness.js
index 0b33615..25044d0 100644
--- a/src/calculateWitness.js
+++ b/src/calculateWitness.js
@@ -223,11 +223,11 @@ class RTCtx {
         return this.witness[sId];
     }
 
-    assert(a,b) {
+    assert(a,b,errStr) {
         const ba = bigInt(a);
         const bb = bigInt(b);
         if (!ba.equals(bb)) {
-            throw new Error("Constraint doesn't match: " + ba.toString() + " != " + bb.toString());
+            throw new Error("Constraint doesn't match "+ this.currentComponent+": "+ errStr + " -> "+ ba.toString() + " != " + bb.toString());
         }
     }
 }