diff -r d382dacfd73f -r 88540bb74300 rt/emul/mini/src/main/java/java/lang/Class.java
--- a/rt/emul/mini/src/main/java/java/lang/Class.java	Tue Feb 26 16:54:16 2013 +0100
+++ b/rt/emul/mini/src/main/java/java/lang/Class.java	Mon Mar 25 16:16:30 2013 +0100
@@ -402,8 +402,15 @@
             }
             return cmpType != null && getComponentType().isAssignableFrom(cmpType);
         }
-        String prop = "$instOf_" + getName().replace('.', '_');
-        return hasCnstrProperty(cls, prop);
+        if (isPrimitive()) {
+            return false;
+        } else {
+            if (cls.isPrimitive()) {
+                return false;
+            }
+            String prop = "$instOf_" + getName().replace('.', '_');
+            return hasCnstrProperty(cls, prop);
+        }
     }
 
     @JavaScriptBody(args = { "who", "prop" }, body =