@@ -750,16 +750,12 @@
 	    BOOL *stop) {
 		[new setObject: block(key, object)
 			forKey: 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.
-	 */
-	new->isa = [OFDictionary class];
+	[new makeImmutable];
+
 	return new;
 }
 
 - (OFDictionary*)filteredDictionaryUsingBlock:
     (of_dictionary_filter_block_t)block
@@ -771,16 +767,12 @@
 		if (block(key, object))
 			[new setObject: object
 				forKey: 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.
-	 */
-	new->isa = [OFDictionary class];
+	[new makeImmutable];
+
 	return new;
 }
 #endif
 
 - (void)dealloc
@@ -857,18 +849,14 @@
 	}
 	[ret replaceOccurrencesOfString: @"\n"
 			     withString: @"\n\t"];
 	[ret appendString: @";\n}"];
 
+	[ret makeImmutable];
+
 	[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;
 }
 
 - (OFXMLElement*)XMLElementBySerializing
 {