Index: src/OFNotificationCenter.h
==================================================================
--- src/OFNotificationCenter.h
+++ src/OFNotificationCenter.h
@@ -20,11 +20,10 @@
 
 @class OFMutableDictionary OF_GENERIC(KeyType, ObjectType);
 #ifdef OF_HAVE_THREADS
 @class OFMutex;
 #endif
-@class OFNotificationCenterHandle;
 
 #ifdef OF_HAVE_BLOCKS
 /**
  * @brief A block which is called when a notification has been posted.
  *
@@ -62,12 +61,12 @@
 /**
  * @brief Adds an observer for the specified notification and object.
  *
  * @param observer The object that should receive notifications
  * @param selector The selector to call on the observer on notifications. The
- *		   method must take exactly one object of type @ref
- *		   OFNotification.
+ *		   method must take exactly one object of type
+ *		   @ref OFNotification.
  * @param name The name of the notification to observe
  * @param object The object that should be sending the notification, or `nil`
  *		 if the object should be ignored to determine what
  *		 notifications to deliver
  */
@@ -101,22 +100,21 @@
  *		 if the object should be ignored to determine what
  *		 notifications to deliver
  * @param block The block to handle notifications
  * @return An opaque object to remove the observer again
  */
-- (OFNotificationCenterHandle *)
-    addObserverForName: (OFNotificationName)name
-		object: (nullable id)object
-	    usingBlock: (OFNotificationCenterBlock)block;
+- (id)addObserverForName: (OFNotificationName)name
+		  object: (nullable id)object
+	      usingBlock: (OFNotificationCenterBlock)block;
 
 /**
  * @brief Removes an observer. The specified observer must be one returned by
  *	  @ref addObserver:selector:name:object:.
  *
  * @param observer The object that was returned when adding the observer
  */
-- (void)removeObserver: (OFNotificationCenterHandle *)observer;
+- (void)removeObserver: (id)observer;
 #endif
 
 /**
  * @brief Posts the specified notification.
  *

Index: src/OFNotificationCenter.m
==================================================================
--- src/OFNotificationCenter.m
+++ src/OFNotificationCenter.m
@@ -245,14 +245,13 @@
 
 	objc_autoreleasePoolPop(pool);
 }
 
 #ifdef OF_HAVE_BLOCKS
-- (OFNotificationCenterHandle *)
-    addObserverForName: (OFNotificationName)name
-		object: (id)object
-	    usingBlock: (OFNotificationCenterBlock)block
+- (id)addObserverForName: (OFNotificationName)name
+		  object: (id)object
+	      usingBlock: (OFNotificationCenterBlock)block
 {
 	void *pool = objc_autoreleasePoolPush();
 	OFNotificationCenterHandle *handle =
 	    [[[OFNotificationCenterHandle alloc] initWithName: name
 						       object: object
@@ -267,13 +266,20 @@
 
 	return [handle autorelease];
 }
 #endif
 
-- (void)removeObserver: (OFNotificationCenterHandle *)handle
+- (void)removeObserver: (id)handle_
 {
-	void *pool = objc_autoreleasePoolPush();
+	OFNotificationCenterHandle *handle;
+	void *pool;
+
+	if (![handle_ isKindOfClass: [OFNotificationCenterHandle class]])
+		@throw [OFInvalidArgumentException exception];
+
+	handle = handle_;
+	pool = objc_autoreleasePoolPush();
 
 	/* {} required to avoid -Wmisleading-indentation false positive. */
 	if (![handle isKindOfClass: [OFNotificationCenterHandle class]]) {
 		@throw [OFInvalidArgumentException exception];
 	}

Index: tests/OFNotificationCenterTests.m
==================================================================
--- tests/OFNotificationCenterTests.m
+++ tests/OFNotificationCenterTests.m
@@ -107,11 +107,11 @@
 	    test1->_received == 1 && test2->_received == 3 &&
 	    test3->_received == 0 && test4->_received == 0)
 
 #ifdef OF_HAVE_BLOCKS
 	__block bool received = false;
-	OFNotificationCenterHandle *handle;
+	id handle;
 
 	notification = [OFNotification notificationWithName: notificationName
 						     object: self];
 	TEST(@"-[addObserverForName:object:usingBlock:]",
 	    (handle = [center addObserverForName: notificationName