diff --git a/rules.module b/rules.module
index 74077c8..3928996 100644
--- a/rules.module
+++ b/rules.module
@@ -352,7 +352,9 @@ function &rules_get_cache($cid = 'data') {
       }
       elseif (strpos($cid, 'event_') === 0) {
         $cache[$cid] = FALSE;
-        RulesEventSet::rebuildEventCache();
+        if (class_exists('RulesEventSet')) {
+          RulesEventSet::rebuildEventCache();
+        }
       }
       else {
         $cache[$cid] = FALSE;