--- a/testing/xpcshell/runxpcshelltests.py
+++ b/testing/xpcshell/runxpcshelltests.py
@@ -785,17 +785,17 @@ class XPCShellTests(object):
           read the xpcshell.ini manifest and set self.alltests to be
           an array of test objects.
 
           if we are chunking tests, it will be done here as well
         """
         if isinstance(self.manifest, manifestparser.TestManifest):
             mp = self.manifest
         else:
-            mp = manifestparser.TestManifest(strict=False)
+            mp = manifestparser.TestManifest(strict=True)
             if self.manifest is None:
                 for testdir in self.testdirs:
                     if testdir:
                         mp.read(os.path.join(testdir, 'xpcshell.ini'))
             else:
                 mp.read(self.manifest)
 
         self.buildTestPath()