@@ -209,11 +209,12 @@
 
 @implementation OFMutableString
 + (void)initialize
 {
 	if (self == [OFMutableString class])
-		placeholder.isa = [OFMutableStringPlaceholder class];
+		object_setClass((id)&placeholder,
+		    [OFMutableStringPlaceholder class]);
 }
 
 + (instancetype)alloc
 {
 	if (self == [OFMutableString class])