@@ -169,16 +169,12 @@
 		@throw [OFInvalidEncodingException newWithClass: isa];
 
 	[ret appendCString: string + last
 		withLength: i - last];
 
-	/*
-	 * 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];
+	[ret makeImmutable];
+
 	return ret;
 }
 
 #ifdef OF_HAVE_BLOCKS
 - (OFString*)stringByXMLUnescapingWithBlock:
@@ -267,15 +263,11 @@
 		@throw [OFInvalidEncodingException newWithClass: isa];
 
 	[ret appendCString: string + last
 		withLength: i - last];
 
-	/*
-	 * 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];
+	[ret makeImmutable];
+
 	return ret;
 }
 #endif
 @end