diff --git a/tools/SourceKit/tools/sourcekitd/bin/XPC/Service/XPCService.cpp b/tools/SourceKit/tools/sourcekitd/bin/XPC/Service/XPCService.cpp
index a66d37644413d..7486a908ed927 100644
--- a/tools/SourceKit/tools/sourcekitd/bin/XPC/Service/XPCService.cpp
+++ b/tools/SourceKit/tools/sourcekitd/bin/XPC/Service/XPCService.cpp
@@ -232,6 +232,7 @@ static std::string getDiagnosticDocumentationPath() {
 }
 
 static dispatch_queue_t msgHandlingQueue;
+static dispatch_queue_t requestQueue;
 
 static void sourcekitdServer_peer_event_handler(xpc_connection_t peer,
                                                 xpc_object_t event) {
@@ -256,66 +257,65 @@ static void sourcekitdServer_peer_event_handler(xpc_connection_t peer,
     assert(type == XPC_TYPE_DICTIONARY);
     // Handle the message
     xpc_retain(event);
-    if (xpc_object_t contents = xpc_dictionary_get_value(event, xpc::KeyMsg)) {
-      assert(xpc_get_type(contents) == XPC_TYPE_ARRAY);
-      sourcekitd_object_t req = xpc_array_get_value(contents, 0);
-
-      void (^handler)(void) = ^{
-        SourceKitCancellationToken cancelToken =
-            reinterpret_cast<SourceKitCancellationToken>(
-                xpc_dictionary_get_uint64(event, xpc::KeyCancelToken));
-        auto Responder = std::make_shared<XPCResponder>(event, peer);
-        xpc_release(event);
-
-        sourcekitd::handleRequest(req, /*CancellationToken=*/cancelToken,
-                                  [Responder](sourcekitd_response_t response) {
-                                    Responder->sendReply(response);
-                                  });
-      };
-
-      if (sourcekitd::requestIsEnableBarriers(req)) {
-        dispatch_barrier_async(msgHandlingQueue, ^{
+    dispatch_async(msgHandlingQueue, ^{
+      if (xpc_object_t contents =
+              xpc_dictionary_get_value(event, xpc::KeyMsg)) {
+        assert(xpc_get_type(contents) == XPC_TYPE_ARRAY);
+        sourcekitd_object_t req = xpc_array_get_value(contents, 0);
+
+        void (^handler)(void) = ^{
+          SourceKitCancellationToken cancelToken =
+              reinterpret_cast<SourceKitCancellationToken>(
+                  xpc_dictionary_get_uint64(event, xpc::KeyCancelToken));
           auto Responder = std::make_shared<XPCResponder>(event, peer);
           xpc_release(event);
-          RequestBarriersEnabled = true;
-          sourcekitd::sendBarriersEnabledResponse([Responder](sourcekitd_response_t response) {
-            Responder->sendReply(response);
+
+          sourcekitd::handleRequest(req, /*CancellationToken=*/cancelToken,
+                                    [Responder](sourcekitd_response_t response) {
+                                      Responder->sendReply(response);
+                                    });
+        };
+
+        if (sourcekitd::requestIsEnableBarriers(req)) {
+          dispatch_barrier_async(requestQueue, ^{
+            auto Responder = std::make_shared<XPCResponder>(event, peer);
+            xpc_release(event);
+            RequestBarriersEnabled = true;
+            sourcekitd::sendBarriersEnabledResponse([Responder](sourcekitd_response_t response) {
+              Responder->sendReply(response);
+            });
           });
-        });
-      } else if (RequestBarriersEnabled && sourcekitd::requestIsBarrier(req)) {
-        dispatch_barrier_async(msgHandlingQueue, handler);
-      } else {
-        dispatch_async(msgHandlingQueue, handler);
-      }
-    } else if (xpc_object_t contents =
-                   xpc_dictionary_get_value(event, "ping")) {
-      dispatch_async(msgHandlingQueue, ^{
+        } else if (RequestBarriersEnabled && sourcekitd::requestIsBarrier(req)) {
+          dispatch_barrier_async(requestQueue, handler);
+        } else {
+          dispatch_async(requestQueue, handler);
+        }
+      } else if (xpc_object_t contents =
+                     xpc_dictionary_get_value(event, "ping")) {
         // Ping back.
         xpc_object_t reply = xpc_dictionary_create_reply(event);
         xpc_release(event);
         assert(reply);
         xpc_connection_send_message(peer, reply);
         xpc_release(reply);
-      });
-    } else if (SourceKitCancellationToken cancelToken =
-                   reinterpret_cast<SourceKitCancellationToken>(
-                       xpc_dictionary_get_uint64(event,
-                                                 xpc::KeyCancelRequest))) {
-      // Execute cancellation on a queue other than `msgHandling` so that we
-      // don’t block the cancellation of a request with a barrier
-      dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
-        sourcekitd::cancelRequest(/*CancellationToken=*/cancelToken);
-      });
-    } else if (SourceKitCancellationToken cancelToken =
-                   reinterpret_cast<SourceKitCancellationToken>(
-                       xpc_dictionary_get_uint64(
-                           event, xpc::KeyDisposeRequestHandle))) {
-      dispatch_async(msgHandlingQueue, ^{
+      } else if (SourceKitCancellationToken cancelToken =
+                     reinterpret_cast<SourceKitCancellationToken>(
+                         xpc_dictionary_get_uint64(event,
+                                                   xpc::KeyCancelRequest))) {
+        // Execute cancellation on a queue other than `msgHandling` so that we
+        // don’t block the cancellation of a request with a barrier
+        dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0), ^{
+          sourcekitd::cancelRequest(/*CancellationToken=*/cancelToken);
+        });
+      } else if (SourceKitCancellationToken cancelToken =
+                     reinterpret_cast<SourceKitCancellationToken>(
+                         xpc_dictionary_get_uint64(
+                             event, xpc::KeyDisposeRequestHandle))) {
         sourcekitd::disposeCancellationToken(/*CancellationToken=*/cancelToken);
-      });
-    } else {
-      assert(false && "unexpected message");
-    }
+      } else {
+        assert(false && "unexpected message");
+      }
+    });
   }
 }
 
@@ -415,9 +415,13 @@ int main(int argc, const char *argv[]) {
     LOG_WARN_FUNC("getrlimit failed: " << llvm::sys::StrError());
   }
 
-  auto attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT,
+  auto msgHandlingQueueAttr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL,
+                                                      QOS_CLASS_DEFAULT, 0);
+  msgHandlingQueue = dispatch_queue_create("message-handling", msgHandlingQueueAttr);
+
+  auto requestQueueAttr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT,
                                                       QOS_CLASS_DEFAULT, 0);
-  msgHandlingQueue = dispatch_queue_create("request-handling", attr);
+  requestQueue = dispatch_queue_create("request-handling", requestQueueAttr);
 
   xpc_main(sourcekitdServer_event_handler);
   return 0;