diff --git a/lib/plugins.py b/lib/plugins.py
index 0c5db2de..a3679d84 100644
--- a/lib/plugins.py
+++ b/lib/plugins.py
@@ -307,6 +307,7 @@ class DeviceMgr(ThreadJob, PrintError):
         self.recognised_hardware = set()
         # For synchronization
         self.lock = threading.RLock()
+        self.hid_lock = threading.RLock()
         self.config = config
 
     def thread_jobs(self):
@@ -490,7 +491,8 @@ class DeviceMgr(ThreadJob, PrintError):
         # wallet libraries are not affected.
         import hid
         self.print_error("scanning devices...")
-        hid_list = hid.enumerate(0, 0)
+        with self.hid_lock:
+            hid_list = hid.enumerate(0, 0)
         # First see what's connected that we know about
         devices = []
         for d in hid_list:
diff --git a/plugins/trezor/plugin.py b/plugins/trezor/plugin.py
index 1f8878af..02823880 100644
--- a/plugins/trezor/plugin.py
+++ b/plugins/trezor/plugin.py
@@ -136,7 +136,8 @@ class TrezorCompatiblePlugin(HW_PluginBase):
         assert self.main_thread != threading.current_thread()
         devmgr = self.device_manager()
         handler = keystore.handler
-        client = devmgr.client_for_keystore(self, handler, keystore, force_pair)
+        with devmgr.hid_lock:
+            client = devmgr.client_for_keystore(self, handler, keystore, force_pair)
         # returns the client for a given keystore. can use xpub
         if client:
             client.used()