diff --git a/rules.module b/rules.module
index daa0faa..4c54486 100644
--- a/rules.module
+++ b/rules.module
@@ -254,7 +254,9 @@ function &rules_get_cache($cid = 'data') {
     }
     elseif (strpos($cid, 'event_') === 0) {
       $cache[$cid] = FALSE;
-      RulesEventSet::rebuildEventCache();
+      if (class_exists('RulesEventSet')) {
+        RulesEventSet::rebuildEventCache();
+      }
       return $cache[$cid];
     }
     else {