@@ -85,16 +85,12 @@
 			withLength: 4];
 
 		break;
 	}
 
-	/*
-	 * 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;
 }
 
 BOOL
 of_base64_decode(OFDataArray *data, const char *string, size_t length)