Index: src/OFObject.m
==================================================================
--- src/OFObject.m
+++ src/OFObject.m
@@ -226,17 +226,12 @@
 
 + (IMP)setImplementation: (IMP)newimp
 	  forClassMethod: (SEL)selector
 {
 #ifdef OF_APPLE_RUNTIME
-	Method method;
-
-	if ((method = class_getClassMethod(self, selector)) == NULL)
-		@throw [OFInvalidArgumentException newWithClass: self
-						       selector: _cmd];
-
-	return method_setImplementation(method, newimp);
+	return class_replaceMethod(self->isa, selector, newimp,
+	    method_getTypeEncoding(class_getClassMethod(self, selector)));
 #else
 	Method_t method;
 	IMP oldimp;
 
 	/* The class method is the instance method of the meta class */
@@ -281,17 +276,12 @@
 
 + (IMP)setImplementation: (IMP)newimp
        forInstanceMethod: (SEL)selector
 {
 #ifdef OF_APPLE_RUNTIME
-	Method method;
-
-	if ((method = class_getInstanceMethod(self, selector)) == NULL)
-		@throw [OFInvalidArgumentException newWithClass: self
-						       selector: _cmd];
-
-	return method_setImplementation(method, newimp);
+	return class_replaceMethod(self, selector, newimp,
+	    method_getTypeEncoding(class_getInstanceMethod(self, selector)));
 #else
 	Method_t method = class_get_instance_method(self, selector);
 	IMP oldimp;
 
 	if (method == NULL)