--- a/dom/media/webrtc/MediaEngineWebRTC.cpp
+++ b/dom/media/webrtc/MediaEngineWebRTC.cpp
@@ -39,34 +39,36 @@ bool AudioInputCubeb::mAnyInUse = false;
 StaticMutex AudioInputCubeb::sMutex;
 uint32_t AudioInputCubeb::sUserChannelCount = 0;
 
 // AudioDeviceID is an annoying opaque value that's really a string
 // pointer, and is freed when the cubeb_device_collection is destroyed
 
 void AudioInputCubeb::UpdateDeviceList()
 {
+  // We keep all the device names, but wipe the mappings and rebuild them.
+  // Do this first so that if cubeb has failed we've unmapped our devices
+  // before we early return. Otherwise we'd keep the old list.
+  for (auto& device_index : (*mDeviceIndexes)) {
+    device_index = -1; // unmapped
+  }
+
   cubeb* cubebContext = CubebUtils::GetCubebContext();
   if (!cubebContext) {
     return;
   }
 
   cubeb_device_collection devices = { nullptr, 0 };
 
   if (CUBEB_OK != cubeb_enumerate_devices(cubebContext,
                                           CUBEB_DEVICE_TYPE_INPUT,
                                           &devices)) {
     return;
   }
 
-  for (auto& device_index : (*mDeviceIndexes)) {
-    device_index = -1; // unmapped
-  }
-  // We keep all the device names, but wipe the mappings and rebuild them
-
   // Calculate translation from existing mDevices to new devices. Note we
   // never end up with less devices than before, since people have
   // stashed indexes.
   // For some reason the "fake" device for automation is marked as DISABLED,
   // so white-list it.
   mDefaultDevice = -1;
   for (uint32_t i = 0; i < devices.count; i++) {
     LOG(("Cubeb device %u: type 0x%x, state 0x%x, name %s, id %p",