@@ -530,16 +530,12 @@
 		[ret appendFormat: @"?%@", query];
 
 	if (fragment != nil)
 		[ret appendFormat: @"#%@", fragment];
 
-	/*
-	 * Class swizzle the string to be immutable. We declared the return type
-	 * to be OFString*, so it can't be modified anyway. But not swizzling it
-	 * would create a real copy each time -[copy] is called.
-	 */
-	ret->isa = [OFString class];
+	[ret makeImmutable];
+
 	return ret;
 }
 
 - (OFString*)description
 {