Index: src/MTXClient.h
==================================================================
--- src/MTXClient.h
+++ src/MTXClient.h
@@ -42,10 +42,17 @@
  *
  * @param exception `nil` on success, otherwise an exception
  */
 typedef void (^mtx_client_response_block_t)(id _Nullable exception);
 
+/**
+ * @brief A block called when an exception occurred during sync.
+ *
+ * @param exception The exception which occurred during sync
+ */
+typedef void (^mtx_sync_exception_handler_block_t)(id exception);
+
 /**
  * @brief A block called when the room list was fetched.
  *
  * @param rooms An array of joined rooms, or nil on error
  * @param exception An exception if fetching the room list failed
@@ -90,10 +97,23 @@
 /**
  * @brief The storage used by the client.
  */
 @property (readonly, nonatomic) id <MTXStorage> storage;
 
+/**
+ * @brief The timeout for sync requests.
+ *
+ * Defaults to 5 minutes.
+ */
+@property (nonatomic) of_time_interval_t syncTimeout;
+
+/**
+ * @brief A block to handle exceptions that occurred during sync.
+ */
+@property (copy, nonatomic)
+    mtx_sync_exception_handler_block_t syncExceptionHandler;
+
 /**
  * @brief Creates a new client with the specified access token on the specified
  *	  homeserver.
  *
  * @param userID The user ID for the client
@@ -141,16 +161,21 @@
 		    homeserver: (OFURL *)homeserver
 		       storage: (id <MTXStorage>)storage
     OF_DESIGNATED_INITIALIZER;
 
 /**
- * @brief Performs a sync.
+ * @brief Starts the sync loop.
+ */
+- (void)startSyncLoop;
+
+/**
+ * @brief Stops the sync loop.
  *
- * @param block A block to call when a sync was performed
+ * The currently waiting sync is not aborted, but after it returns, no new sync
+ * will be started.
  */
-- (void)syncWithTimeout: (of_time_interval_t)timeout
-		  block: (mtx_client_response_block_t)block;
+- (void)stopSyncLoop;
 
 /**
  * @brief Logs out the device and invalidates the access token.
  *
  * @warning The client can no longer be used after this succeeded!

Index: src/MTXClient.m
==================================================================
--- src/MTXClient.m
+++ src/MTXClient.m
@@ -46,10 +46,14 @@
 	    homeserver.query != nil || homeserver.fragment != nil)
 		@throw [OFInvalidArgumentException exception];
 }
 
 @implementation MTXClient
+{
+	bool _syncing;
+}
+
 + (instancetype)clientWithUserID: (OFString *)userID
 			deviceID: (OFString *)deviceID
 		     accessToken: (OFString *)accessToken
 		      homeserver: (OFURL *)homeserver
 			 storage: (id <MTXStorage>)storage
@@ -156,10 +160,11 @@
 		_userID = [userID copy];
 		_deviceID = [deviceID copy];
 		_accessToken = [accessToken copy];
 		_homeserver = [homeserver copy];
 		_storage = [storage retain];
+		_syncTimeout = 300;
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}
 
@@ -194,40 +199,48 @@
 	return [MTXRequest requestWithPath: path
 			       accessToken: _accessToken
 				homeserver: _homeserver];
 }
 
-- (void)syncWithTimeout: (of_time_interval_t)timeout
-		  block: (mtx_client_response_block_t)block
+- (void)startSyncLoop
 {
+	if (_syncing)
+		return;
+
+	_syncing = true;
+
 	void *pool = objc_autoreleasePoolPush();
 	MTXRequest *request = [self
 	    requestWithPath: @"/_matrix/client/r0/sync"];
-	unsigned long long timeoutMs = timeout * 1000;
+	unsigned long long timeoutMs = _syncTimeout * 1000;
 	OFMutableDictionary<OFString *, OFString *> *query =
 	    [OFMutableDictionary dictionaryWithObject: @(timeoutMs).stringValue
 					       forKey: @"timeout"];
 	query[@"since"] = [_storage nextBatchForDeviceID: _deviceID];
 	request.query = query;
 	[request performWithBlock: ^ (mtx_response_t response, int statusCode,
 				       id exception) {
 		if (exception != nil) {
-			block(exception);
+			if (_syncExceptionHandler != NULL)
+				_syncExceptionHandler(exception);
 			return;
 		}
 
 		if (statusCode != 200) {
-			block([MTXSyncFailedException
-			    exceptionWithStatusCode: statusCode
-					   response: response
-					     client: self]);
+			if (_syncExceptionHandler != NULL)
+				_syncExceptionHandler([MTXSyncFailedException
+				    exceptionWithStatusCode: statusCode
+						   response: response
+						     client: self]);
 			return;
 		}
 
 		OFString *nextBatch = response[@"next_batch"];
 		if (![nextBatch isKindOfClass: OFString.class]) {
-			block([OFInvalidServerReplyException exception]);
+			if (_syncExceptionHandler != NULL)
+				_syncExceptionHandler(
+				    [OFInvalidServerReplyException exception]);
 			return;
 		}
 
 		@try {
 			[_storage transactionWithBlock: ^ {
@@ -243,19 +256,26 @@
 				    response[@"to_device"]];
 
 				return true;
 			}];
 		} @catch (id e) {
-			block(e);
+			if (_syncExceptionHandler != NULL)
+				_syncExceptionHandler(e);
 			return;
 		}
 
-		block(nil);
+		if (_syncing)
+			[self startSyncLoop];
 	}];
 
 	objc_autoreleasePoolPop(pool);
 }
+
+- (void)stopSyncLoop
+{
+	_syncing = false;
+}
 
 - (void)logOutWithBlock: (mtx_client_response_block_t)block
 {
 	void *pool = objc_autoreleasePoolPush();
 	MTXRequest *request =

Index: tests/tests.m
==================================================================
--- tests/tests.m
+++ tests/tests.m
@@ -61,25 +61,11 @@
 		}
 
 		_client = [client retain];
 		of_log(@"Logged in client: %@", _client);
 
-		[self sync];
-	}];
-}
-
-- (void)sync
-{
-	[_client syncWithTimeout: 5
-			   block: ^ (id exception) {
-		if (exception != nil) {
-			of_log(@"Failed to sync: %@", exception);
-			[OFApplication terminateWithStatus: 1];
-		}
-
-		of_log(@"Synced");
-
+		[_client startSyncLoop];
 		[self fetchRoomList];
 	}];
 }
 
 - (void)fetchRoomList
@@ -108,25 +94,10 @@
 		}
 
 		_roomID = [roomID copy];
 		of_log(@"Joined room %@", _roomID);
 
-		[self sync2];
-	}];
-}
-
-- (void)sync2
-{
-	[_client syncWithTimeout: 5
-			   block: ^ (id exception) {
-		if (exception != nil) {
-			of_log(@"Failed to sync: %@", exception);
-			[OFApplication terminateWithStatus: 1];
-		}
-
-		of_log(@"Synced");
-
 		[self sendMessage];
 	}];
 }
 
 - (void)sendMessage
@@ -140,11 +111,15 @@
 			[OFApplication terminateWithStatus: 1];
 		}
 
 		of_log(@"Message sent to %@", _roomID);
 
-		[self leaveRoom];
+		of_log(
+		    @"Waiting 5 seconds before leaving room and logging out");
+
+		[self performSelector: @selector(leaveRoom)
+			   afterDelay: 5];
 	}];
 }
 
 - (void)leaveRoom
 {