@@ -35,11 +35,11 @@
 	OFXMLElement *root;
 	OFString *ret;
 
 	if (![self conformsToProtocol: @protocol(OFSerialization)])
 		@throw [OFNotImplementedException
-		    exceptionWithClass: isa
+		    exceptionWithClass: [self class]
 			      selector: @selector(stringBySerializing)];
 
 	pool = [[OFAutoreleasePool alloc] init];
 	element = [(id)self XMLElementBySerializing];