diff --git a/tests/test_update.py b/tests/test_update.py
index 76b2b95cce..bd409477d7 100644
--- a/tests/test_update.py
+++ b/tests/test_update.py
@@ -123,3 +123,11 @@ class UpdateTest(testtools.TestCase):
         returncode = subprocess.call([sys.executable, "update.py",
                                      "bad_project"])
         self.assertEqual(returncode, 1)
+
+    def test_requirment_not_in_global_non_fatal(self):
+        env = os.environ.copy()
+        env['NON_STANDARD_REQS'] = '1'
+        returncode = subprocess.call(
+            [sys.executable, "update.py", "bad_project"],
+            env=env)
+        self.assertEqual(returncode, 0)
diff --git a/update.py b/update.py
index 0cf9ef2e3f..ea7f35ba98 100644
--- a/update.py
+++ b/update.py
@@ -135,12 +135,19 @@ def _sync_requirements_file(source_reqs, dev_reqs, dest_path, suffix):
                 else:
                     new_reqs.write("%s\n" % source_reqs[old_pip])
             else:
-                # Found a requirement that isn't in the global requirement file
-                # This is not supposed to happen, so exit with a failure.
-                print("'%s' is not a global requirement but it should be,"
-                      "something went wrong" %
-                      old_pip)
-                sys.exit(1)
+                # What do we do if we find something unexpected?
+                #
+                # In the default cause we should die horribly, because
+                # the point of global requirements was a single lever
+                # to control all the pip installs in the gate.
+                #
+                # However, we do have other projects using
+                # devstack jobs that might have legitimate reasons to
+                # override. For those we support NON_STANDARD_REQS=1
+                # environment variable to turn this into a warning only.
+                print("'%s' is not in global-requirements.txt" % old_pip)
+                if os.getenv('NON_STANDARD_REQS', '0') != '1':
+                    sys.exit(1)
 
 
 def _copy_requires(suffix, dest_dir):