Index: src/OFSerialization.h
==================================================================
--- src/OFSerialization.h
+++ src/OFSerialization.h
@@ -15,10 +15,11 @@
 
 #import "OFObject.h"
 
 OF_ASSUME_NONNULL_BEGIN
 
+@class OFConstantString;
 @class OFXMLElement;
 
 /**
  * @protocol OFSerialization OFSerialization.h ObjFW/OFSerialization.h
  *
@@ -40,11 +41,11 @@
 @end
 
 #ifdef __cplusplus
 extern "C" {
 #endif
-extern OFString *const OFSerializationNS;
+extern OFConstantString *const OFSerializationNS;
 #ifdef __cplusplus
 }
 #endif
 
 OF_ASSUME_NONNULL_END

Index: src/OFSerialization.m
==================================================================
--- src/OFSerialization.m
+++ src/OFSerialization.m
@@ -12,8 +12,8 @@
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
 #import "OFSerialization.h"
-#import "OFString.h"
 
-OFString *const OFSerializationNS = @"https://objfw.nil.im/serialization";
+OFConstantString *const OFSerializationNS =
+    @"https://objfw.nil.im/serialization";