@@ -616,11 +616,11 @@
 + (void)initialize
 {
 	if (self != [OFString class])
 		return;
 
-	placeholder.isa = [OFStringPlaceholder class];
+	object_setClass((id)&placeholder, [OFStringPlaceholder class]);
 
 #if defined(HAVE_STRTOF_L) || defined(HAVE_STRTOD_L) || defined(HAVE_USELOCALE)
 	if ((cLocale = newlocale(LC_ALL_MASK, "C", NULL)) == NULL)
 		@throw [OFInitializationFailedException
 		    exceptionWithClass: self];
@@ -801,11 +801,12 @@
 					   encoding: encoding] autorelease];
 }
 
 - (instancetype)init
 {
-	if ([self isMemberOfClass: [OFString class]]) {
+	if ([self isMemberOfClass: [OFString class]] ||
+	    [self isMemberOfClass: [OFMutableString class]]) {
 		@try {
 			[self doesNotRecognizeSelector: _cmd];
 		} @catch (id e) {
 			[self release];
 			@throw e;