diff --git a/artiq/frontend/artiq_master.py b/artiq/frontend/artiq_master.py
index 1d3a8617e..94c8903c7 100755
--- a/artiq/frontend/artiq_master.py
+++ b/artiq/frontend/artiq_master.py
@@ -95,7 +95,7 @@ def main():
         "master_dataset_db": dataset_db,
         "master_schedule": scheduler,
         "master_experiment_db": experiment_db
-    })
+    }, allow_parallel=True)
     loop.run_until_complete(server_control.start(
         bind, args.port_control))
     atexit_register_coroutine(server_control.stop)
diff --git a/artiq/protocols/pc_rpc.py b/artiq/protocols/pc_rpc.py
index c9f53b286..512237d60 100644
--- a/artiq/protocols/pc_rpc.py
+++ b/artiq/protocols/pc_rpc.py
@@ -433,6 +433,12 @@ class Server(_AsyncioServer):
     simple cases: it allows new connections to be be accepted even when the
     previous client failed to properly shut down its connection.
 
+    If a target method is a coroutine, it is awaited and its return value
+    is sent to the RPC client. If ``allow_parallel`` is true, multiple
+    target coroutines may be executed in parallel (one per RPC client),
+    otherwise a lock ensures that the calls from several clients are executed
+    sequentially.
+
     :param targets: A dictionary of objects providing the RPC methods to be
         exposed to the client. Keys are names identifying each object.
         Clients select one of these objects using its name upon connection.
@@ -442,14 +448,74 @@ class Server(_AsyncioServer):
         ``terminate`` method that unblocks any tasks waiting on
         ``wait_terminate``. This is useful to handle server termination
         requests from clients.
+    :param allow_parallel: Allow concurrent asyncio calls to the target's
+        methods.
     """
-    def __init__(self, targets, description=None, builtin_terminate=False):
+    def __init__(self, targets, description=None, builtin_terminate=False,
+                 allow_parallel=False):
         _AsyncioServer.__init__(self)
         self.targets = targets
         self.description = description
         self.builtin_terminate = builtin_terminate
         if builtin_terminate:
             self._terminate_request = asyncio.Event()
+        if allow_parallel:
+            self._noparallel = None
+        else:
+            self._noparallel = asyncio.Lock()
+
+    async def _process_action(self, target, obj):
+        if self._noparallel is not None:
+            await self._noparallel.acquire()
+        try:
+            if obj["action"] == "get_rpc_method_list":
+                members = inspect.getmembers(target, inspect.ismethod)
+                doc = {
+                    "docstring": inspect.getdoc(target),
+                    "methods": {}
+                }
+                for name, method in members:
+                    if name.startswith("_"):
+                        continue
+                    method = getattr(target, name)
+                    argspec = inspect.getfullargspec(method)
+                    doc["methods"][name] = (dict(argspec._asdict()),
+                                            inspect.getdoc(method))
+                if self.builtin_terminate:
+                    doc["methods"]["terminate"] = (
+                        {
+                            "args": ["self"],
+                            "defaults": None,
+                            "varargs": None,
+                            "varkw": None,
+                            "kwonlyargs": [],
+                            "kwonlydefaults": [],
+                        },
+                        "Terminate the server.")
+                return {"status": "ok", "ret": doc}
+            elif obj["action"] == "call":
+                logger.debug("calling %s", _PrettyPrintCall(obj))
+                if (self.builtin_terminate and obj["name"] ==
+                        "terminate"):
+                    self._terminate_request.set()
+                    return {"status": "ok", "ret": None}
+                else:
+                    method = getattr(target, obj["name"])
+                    ret = method(*obj["args"], **obj["kwargs"])
+                    if inspect.iscoroutine(ret):
+                        ret = await ret
+                    return {"status": "ok", "ret": ret}
+            else:
+                raise ValueError("Unknown action: {}"
+                                 .format(obj["action"]))
+        except asyncio.CancelledError:
+            raise
+        except:
+            return {"status": "failed",
+                    "message": traceback.format_exc()}
+        finally:
+            if self._noparallel is not None:
+                self._noparallel.release()
 
     async def _handle_connection_cr(self, reader, writer):
         try:
@@ -476,53 +542,8 @@ class Server(_AsyncioServer):
                 line = await reader.readline()
                 if not line:
                     break
-                obj = pyon.decode(line.decode())
-                try:
-                    if obj["action"] == "get_rpc_method_list":
-                        members = inspect.getmembers(target, inspect.ismethod)
-                        doc = {
-                            "docstring": inspect.getdoc(target),
-                            "methods": {}
-                        }
-                        for name, method in members:
-                            if name.startswith("_"):
-                                continue
-                            method = getattr(target, name)
-                            argspec = inspect.getfullargspec(method)
-                            doc["methods"][name] = (dict(argspec._asdict()),
-                                                    inspect.getdoc(method))
-                        if self.builtin_terminate:
-                            doc["methods"]["terminate"] = (
-                                {
-                                    "args": ["self"],
-                                    "defaults": None,
-                                    "varargs": None,
-                                    "varkw": None,
-                                    "kwonlyargs": [],
-                                    "kwonlydefaults": [],
-                                },
-                                "Terminate the server.")
-                        obj = {"status": "ok", "ret": doc}
-                    elif obj["action"] == "call":
-                        logger.debug("calling %s", _PrettyPrintCall(obj))
-                        if (self.builtin_terminate and obj["name"] ==
-                                "terminate"):
-                            self._terminate_request.set()
-                            obj = {"status": "ok", "ret": None}
-                        else:
-                            method = getattr(target, obj["name"])
-                            ret = method(*obj["args"], **obj["kwargs"])
-                            if inspect.iscoroutine(ret):
-                                ret = await ret
-                            obj = {"status": "ok", "ret": ret}
-                    else:
-                        raise ValueError("Unknown action: {}"
-                                         .format(obj["action"]))
-                except Exception:
-                    obj = {"status": "failed",
-                           "message": traceback.format_exc()}
-                line = pyon.encode(obj) + "\n"
-                writer.write(line.encode())
+                reply = await self._process_action(target, pyon.decode(line.decode()))
+                writer.write((pyon.encode(reply) + "\n").encode())
         except (ConnectionResetError, ConnectionAbortedError, BrokenPipeError):
             # May happens on Windows when client disconnects
             pass