@@ -20,10 +20,13 @@
 
 OF_ASSUME_NONNULL_BEGIN
 
 @class OFMutableArray OF_GENERIC(ObjectType);
 @class OFDate;
+#ifdef OF_HAVE_THREADS
+@class OFMutex;
+#endif
 
 /*!
  * @protocol OFKernelEventObserverDelegate
  *	     OFKernelEventObserver.h ObjFW/OFKernelEventObserver.h
  *
@@ -113,10 +116,13 @@
 #ifdef OF_HAVE_PIPE
 	int _cancelFD[2];
 #else
 	of_socket_t _cancelFD[2];
 	struct sockaddr_in _cancelAddr;
+#endif
+#ifdef OF_HAVE_THREADS
+	OFMutex *_mutex;
 #endif
 }
 
 #ifdef OF_HAVE_PROPERTIES
 @property OF_NULLABLE_PROPERTY (assign)