@@ -80,11 +80,12 @@
 	}
 
 	if (unescape)
 		return [ret stringByXMLUnescapingWithDelegate: delegate];
 
-	ret->isa = [OFString class];
+	[ret makeImmutable];
+
 	return ret;
 }
 
 static OFString*
 namespace_for_prefix(OFString *prefix, OFArray *namespaces)
@@ -792,11 +793,11 @@
 
 	cacheString = [OFMutableString stringWithCString: [cache cArray]
 						  length: [cache count]];
 	[cacheString deleteEnclosingWhitespaces];
 	/* Prevent a useless copy later */
-	cacheString->isa = [OFString class];
+	[cacheString makeImmutable];
 
 	cacheCString = [cacheString cString];
 	cacheLength = [cacheString cStringLength];
 
 	if ((tmp = memchr(cacheCString, ':', cacheLength)) != NULL) {