diff --git a/moo/kernel/test-003.moo b/moo/kernel/test-003.moo
index c5962fd..435dfc2 100644
--- a/moo/kernel/test-003.moo
+++ b/moo/kernel/test-003.moo
@@ -54,7 +54,7 @@ class MyObject(TestObject)
 	method(#class) main
 	{
 		| tc limit |
-		
+(10 isKindOf: 20) dump.
 		tc := %(
 			## 0 - 4
 			[(Object isKindOf: Class) == true],
@@ -63,9 +63,11 @@ class MyObject(TestObject)
 			[(Class isKindOf: Apex) == true],
 			[(Class isKindOf: Object) == false],
 
+			## 5-9
 			[(Apex isKindOf: Class) == true],
 			[(SmallInteger isKindOf: Integer) == false],
 			[(10 isKindOf: Integer) == true],
+			[(10 isKindOf: 20) == false],
 
 			[(Apex isMemberOf: Class) == true],
 			[(Class isMemberOf: Class) == true]
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index fc54073..37c8a17 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -2105,9 +2105,8 @@ static moo_pfrc_t pf_is_kind_of (moo_t* moo, moo_ooi_t nargs)
 	rcv = MOO_STACK_GETRCV(moo, nargs);
 	_class = MOO_STACK_GETARG(moo, nargs, 0);
 
-	MOO_PF_CHECK_ARGS (moo, nargs, MOO_CLASSOF(moo, _class) == moo->_class);
-
-	if (moo_iskindof(moo, rcv, (moo_oop_class_t)_class))
+	if (MOO_CLASSOF(moo, _class) == moo->_class &&
+	    moo_iskindof(moo, rcv, (moo_oop_class_t)_class))
 	{
 		MOO_STACK_SETRET (moo, nargs, moo->_true);
 	}
diff --git a/moo/lib/moo.c b/moo/lib/moo.c
index 29adb76..aefcdc4 100644
--- a/moo/lib/moo.c
+++ b/moo/lib/moo.c
@@ -978,6 +978,8 @@ int moo_iskindof (moo_t* moo, moo_oop_t obj, moo_oop_class_t _class)
 {
 	moo_oop_class_t c;
 
+	MOO_ASSERT (moo, MOO_CLASSOF(moo,_class) == moo->_class);
+
 	c = MOO_CLASSOF(moo,obj); /* c := self class */
 	if (c == moo->_class) 
 	{