diff --git a/lib/ClassBuilder.js b/lib/ClassBuilder.js
index 74f2dc4..0b760aa 100644
--- a/lib/ClassBuilder.js
+++ b/lib/ClassBuilder.js
@@ -244,14 +244,16 @@ exports.isInstanceOf = function( type, instance )
         return false;
     }
 
-    // check prototype chain (will throw an error if type is not a
-    // constructor (function)
-    if ( ( typeof type === 'function' )
-        && ( instance instanceof type )
-    )
+    try
     {
-        return true;
+        // check prototype chain (will throw an error if type is not a
+        // constructor (function)
+        if ( instance instanceof type )
+        {
+            return true;
+        }
     }
+    catch ( e ) {}
 
     // if no metadata is available, then our remaining checks cannot be
     // performed