diff --git a/repos/os/src/drivers/usb_block/main.cc b/repos/os/src/drivers/usb_block/main.cc
index 1b7c5f8020..5f4f4f2572 100644
--- a/repos/os/src/drivers/usb_block/main.cc
+++ b/repos/os/src/drivers/usb_block/main.cc
@@ -64,7 +64,7 @@ struct Usb::Block_driver : Usb::Completion
 		size_t         size      { 0 };
 		bool           completed { false };
 
-		Block_request(Request &request, Request_stream::Payload const &payload)
+		Block_request(Request const &request, Request_stream::Payload const &payload)
 		: block_request(request)
 		{
 			payload.with_content(request, [&](void *addr, size_t sz) {
@@ -902,12 +902,20 @@ struct Usb::Block_driver : Usb::Completion
 		         .writeable   = _writeable };
 	}
 
-	Response submit(Request &block_request,
+	Response submit(Request                 const &block_request,
 	                Request_stream::Payload const &payload)
 	{
 		if (device_plugged == false)
 			return Response::REJECTED;
 
+		/*
+		 * Check if there is already a request pending and wait
+		 * until it has finished. We do this check here to implement
+		 * 'SYNC' as barrier that waits for out-standing requests.
+		 */
+		if (request_pending())
+			return Response::RETRY;
+
 		Operation const &op = block_request.operation;
 
 		/* read only */
@@ -924,12 +932,16 @@ struct Usb::Block_driver : Usb::Completion
 		if (!force_cmd_16 && last >= ~0U)
 			return Response::REJECTED;
 
-		/* check if request is pending */
-		if (request_pending())
-			return Response::RETRY;
-
 		request.construct(block_request, payload);
 
+		/* operations currently handled as successful NOP */
+		if (request->block_request.operation.type == Operation::Type::TRIM
+		 || request->block_request.operation.type == Operation::Type::SYNC) {
+			request->block_request.success = true;
+			request->completed             = true;
+			return Response::ACCEPTED;
+		}
+
 		/* execute */
 		send_cbw(op.block_number, op.count, request->read());
 
@@ -1000,28 +1012,31 @@ struct Usb::Main : Rpc_object<Typed_root<Block::Session>>
 	{
 		if (!block_session.constructed()) return;
 
-		/* ack and release possibly pending packet */
-		block_session->try_acknowledge([&] (Block_session_component::Ack &ack) {
-			driver.with_completed([&] (Block::Request &request) {
-				ack.submit(request);
+		bool progress;
+		do {
+			progress = false;
+
+			/* ack and release possibly pending packet */
+			block_session->try_acknowledge([&] (Block_session_component::Ack &ack) {
+				driver.with_completed([&] (Block::Request const &request) {
+					ack.submit(request);
+					progress = true;
+				});
 			});
-		});
 
-		block_session->with_requests([&] (Request request) {
+			block_session->with_requests([&] (Request const request) {
 
-			/* only read/write for now */
-			if (Operation::has_payload(request.operation.type) == false) {
-				request.success = true;
-				return Response::REJECTED;
-			}
+				Response response = Response::RETRY;
 
-			Response response = Response::RETRY;
+				block_session->with_payload([&] (Request_stream::Payload const &payload) {
+					response = driver.submit(request, payload);
+				});
+				if (response != Response::RETRY)
+					progress = true;
 
-			block_session->with_payload([&] (Request_stream::Payload const &payload) {
-				response = driver.submit(request, payload);
+				return response;
 			});
-			return response;
-		});
+		} while (progress);
 
 		block_session->wakeup_client_if_needed();
 	}