@@ -618,10 +618,16 @@
 	for (i = 0; i < size; i++)
 		if (data[i] != NULL && data[i] != DELETED)
 			[dict setObject: block(data[i]->key, data[i]->object)
 				 forKey: data[i]->key];
 
+	/*
+	 * Class swizzle the dictionary to be immutable. We declared the return
+	 * type to be OFDictionary*, so it can't be modified anyway. But not
+	 * swizzling it would create a real copy each time -[copy] is called.
+	 */
+	dict->isa = [OFDictionary class];
 	return dict;
 }
 
 - (OFDictionary*)filteredDictionaryUsingBlock:
     (of_dictionary_filter_block_t)block
@@ -633,10 +639,16 @@
 		if (data[i] != NULL && data[i] != DELETED)
 			if (block(data[i]->key, data[i]->object))
 				[dict setObject: data[i]->object
 					 forKey: data[i]->key];
 
+	/*
+	 * Class swizzle the dictionary to be immutable. We declared the return
+	 * type to be OFDictionary*, so it can't be modified anyway. But not
+	 * swizzling it would create a real copy each time -[copy] is called.
+	 */
+	dict->isa = [OFDictionary class];
 	return dict;
 }
 #endif
 
 - (void)dealloc
@@ -704,10 +716,16 @@
 	}
 	[ret appendString: @"}"];
 
 	[pool release];
 
+	/*
+	 * 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];
 	return ret;
 }
 @end
 
 @implementation OFDictionaryEnumerator