--- a/testing/mochitest/mach_commands.py
+++ b/testing/mochitest/mach_commands.py
@@ -734,17 +734,20 @@ class MachCommands(MachCommandBase):
         return mochitest.run_desktop_test(self._mach_context,
             test_paths=test_paths, suite=flavor, **kwargs)
 
 
 # TODO For now b2g commands will only work with the emulator,
 # they should be modified to work with all devices.
 def is_emulator(cls):
     """Emulator needs to be configured."""
-    return cls.device_name.startswith('emulator')
+    try:
+        return cls.device_name.startswith('emulator')
+    except AttributeError:
+        return False
 
 
 @CommandProvider
 class B2GCommands(MachCommandBase):
     """So far these are only mochitest plain. They are
     implemented separately because their command lines
     are completely different.
     """