diff --git a/dbus/controller.c b/dbus/controller.c
index 033fb65e..ce0f1ec9 100644
--- a/dbus/controller.c
+++ b/dbus/controller.c
@@ -330,15 +330,17 @@ jack_controller_switch_master(
     struct jack_controller * controller_ptr,
     void *dbus_call_context_ptr)
 {
+    assert(controller_ptr->started); /* should be ensured by caller */
+
     if (!jackctl_server_switch_master(
             controller_ptr->server,
             jack_params_get_driver(controller_ptr->params)))
     {
         jack_dbus_error(dbus_call_context_ptr, JACK_DBUS_ERROR_GENERIC, "Failed to switch master");
+        controller_ptr->started = false;
         return FALSE;
     }
 
-
     return TRUE;
 }
 
@@ -390,10 +392,10 @@ on_device_release(const char * device_name)
 
     // Look for corresponding reserved device
     for (i = 0; i < DEVICE_MAX; i++) {
- 	if (strcmp(g_reserved_device[i].device_name, device_name) == 0)  
+ 	if (strcmp(g_reserved_device[i].device_name, device_name) == 0)
 	    break;
     }
-   
+
     if (i < DEVICE_MAX) {
 	jack_info("Released audio card %s", device_name);
         rd_release(g_reserved_device[i].reserved_device);
diff --git a/dbus/controller_iface_control.c b/dbus/controller_iface_control.c
index a82cbcd7..c1e18956 100644
--- a/dbus/controller_iface_control.c
+++ b/dbus/controller_iface_control.c
@@ -122,11 +122,18 @@ jack_control_run_method(
     }
     else if (strcmp (call->method_name, "SwitchMaster") == 0)
     {
-        if (!jack_controller_switch_master(controller_ptr, call))
+        if (!controller_ptr->started)
         {
-            /* the reply is set by the failed function */
-            assert(call->reply != NULL);
-            return true;
+            goto not_started;
+        }
+        else
+        {
+            if (!jack_controller_switch_master(controller_ptr, call))
+            {
+                /* the reply is set by the failed function */
+                assert(call->reply != NULL);
+                return true;
+            }
         }
     }
     else if (strcmp (call->method_name, "GetLoad") == 0)
@@ -220,7 +227,7 @@ jack_control_run_method(
             */
             goto exit;
         }
-    
+
         if (!jack_controller_load_internal(controller_ptr, internal_name)) {
             jack_dbus_error(
                 call,
@@ -244,7 +251,7 @@ jack_control_run_method(
             */
             goto exit;
         }
-        
+
         if (!jack_controller_add_slave_driver(controller_ptr, driver_name))
         {
             jack_dbus_error(
@@ -273,7 +280,7 @@ jack_control_run_method(
             */
             goto exit;
         }
-        
+
         if (!jack_controller_remove_slave_driver(controller_ptr, driver_name))
         {
             jack_dbus_error(
@@ -297,7 +304,7 @@ jack_control_run_method(
             */
             goto exit;
         }
-        
+
         if (!jack_controller_unload_internal(controller_ptr, internal_name)) {
             jack_dbus_error(
                 call,