diff --git a/ldclient/client.py b/ldclient/client.py
index d635e09c..683a5c3b 100644
--- a/ldclient/client.py
+++ b/ldclient/client.py
@@ -321,6 +321,8 @@ def all_flags_state(self, user, **kwargs):
         with_reasons = kwargs.get('with_reasons', False)
         try:
             flags_map = self._store.all(FEATURES, lambda x: x)
+            if flags_map is None:
+                raise ValueError("feature store error")
         except Exception as e:
             log.error("Unable to read flags for all_flag_state: %s" % e)
             return FeatureFlagsState(False)