--- a/testing/xpcshell/mach_commands.py
+++ b/testing/xpcshell/mach_commands.py
@@ -24,16 +24,22 @@ from mach.decorators import (
 
 
 if sys.version_info[0] < 3:
     unicode_type = unicode
 else:
     unicode_type = str
 
 
+# This should probably be consolidated with similar classes in other test
+# runners.
+class InvalidTestPathError(Exception):
+    """Exception raised when the test path is not valid."""
+
+
 class XPCShellRunner(MozbuildObject):
     """Run xpcshell tests."""
     def run_suite(self, **kwargs):
         manifest = os.path.join(self.topobjdir, '_tests', 'xpcshell',
             'xpcshell.ini')
 
         self._run_xpcshell_harness(manifest=manifest, **kwargs)
 
@@ -53,16 +59,24 @@ class XPCShellRunner(MozbuildObject):
         relative_dir = test_file
 
         if test_file.startswith(self.topsrcdir):
             relative_dir = test_file[len(self.topsrcdir):]
 
         test_dir = os.path.join(self.topobjdir, '_tests', 'xpcshell',
                 os.path.dirname(relative_dir))
 
+        xpcshell_ini_file = os.path.join(test_dir, 'xpcshell.ini')
+        if not os.path.exists(xpcshell_ini_file):
+            raise InvalidTestPathError('An xpcshell.ini could not be found '
+                'for the passed test path. Please select a path whose '
+                'directory contains an xpcshell.ini file. It is possible you '
+                'received this error because the tree is not built or tests '
+                'are not enabled.')
+
         args = {
             'debug': debug,
             'interactive': interactive,
             'keep_going': keep_going,
             'shuffle': shuffle,
             'test_dirs': [test_dir],
         }
 
@@ -148,10 +162,15 @@ class MachCommands(MachCommandBase):
         help='Randomize the execution order of tests.')
     def run_xpcshell_test(self, **params):
         # We should probably have a utility function to ensure the tree is
         # ready to run tests. Until then, we just create the state dir (in
         # case the tree wasn't built with mach).
         self._ensure_state_subdir_exists('.')
 
         xpcshell = self._spawn(XPCShellRunner)
-        xpcshell.run_test(**params)
 
+        try:
+            return xpcshell.run_test(**params)
+        except InvalidTestPathError as e:
+            print(e.message)
+            return 1
+