diff --git a/google/oauth2/credentials.py b/google/oauth2/credentials.py
index 4ad52db90..41f4a05bb 100644
--- a/google/oauth2/credentials.py
+++ b/google/oauth2/credentials.py
@@ -160,9 +160,11 @@ def __getstate__(self):
         # unpickling certain callables (lambda, functools.partial instances)
         # because they need to be importable.
         # Instead, the refresh_handler setter should be used to repopulate this.
-        del state_dict["_refresh_handler"]
-        # Remove worker as it contains multiproccessing queue objects.
-        del state_dict["_refresh_worker"]
+        if "_refresh_handler" in state_dict:
+            del state_dict["_refresh_handler"]
+
+        if "_refresh_worker" in state_dict:
+            del state_dict["_refresh_worker"]
         return state_dict
 
     def __setstate__(self, d):
@@ -186,7 +188,7 @@ def __setstate__(self, d):
         # The refresh_handler setter should be used to repopulate this.
         self._refresh_handler = None
         self._refresh_worker = None
-        self._use_non_blocking_refresh = d.get("_use_non_blocking_refresh")
+        self._use_non_blocking_refresh = d.get("_use_non_blocking_refresh", False)
 
     @property
     def refresh_token(self):
diff --git a/system_tests/secrets.tar.enc b/system_tests/secrets.tar.enc
index 493b2222e..c5b080e8b 100644
Binary files a/system_tests/secrets.tar.enc and b/system_tests/secrets.tar.enc differ
diff --git a/tests/oauth2/test_credentials.py b/tests/oauth2/test_credentials.py
index 78711299e..7516fe22e 100644
--- a/tests/oauth2/test_credentials.py
+++ b/tests/oauth2/test_credentials.py
@@ -963,6 +963,8 @@ def test_pickle_with_missing_attribute(self):
         # this mimics a pickle created with a previous class definition with
         # fewer attributes
         del creds.__dict__["_quota_project_id"]
+        del creds.__dict__["_refresh_handler"]
+        del creds.__dict__["_refresh_worker"]
 
         unpickled = pickle.loads(pickle.dumps(creds))