diff --git a/management/univention-directory-notifier/src/notify.c b/management/univention-directory-notifier/src/notify.c
index f7eb26562b..2967ef4d32 100644
--- a/management/univention-directory-notifier/src/notify.c
+++ b/management/univention-directory-notifier/src/notify.c
@@ -423,7 +423,10 @@ char* notify_transcation_get_one_dn ( unsigned long last_known_id )
 	memset(buffer, 0, sizeof(buffer));
 
 	if ((pos = index_get(index, last_known_id)) >= 0) {
-		fseek(notify.tf, pos, SEEK_SET);
+		if (fseek(notify.tf, pos, SEEK_SET) != 0) {
+			univention_debug(UV_DEBUG_TRANSFILE, UV_DEBUG_WARN, "invalid transaction index");
+			index_invalidate(notify.tf);
+		}
 		if (fgets(buffer, sizeof(buffer), notify.tf) != NULL) {
 			univention_debug(UV_DEBUG_TRANSFILE, UV_DEBUG_ALL, "BUFFER=%s", buffer);
 			if ( buffer[strlen(buffer)-1] == '\n' ) {
@@ -433,6 +436,9 @@ char* notify_transcation_get_one_dn ( unsigned long last_known_id )
 			if (id == last_known_id) {
 				found = true;
 				univention_debug(UV_DEBUG_TRANSFILE, UV_DEBUG_INFO, "Found (get_one_dn, index) %ld",id);
+			} else {
+				univention_debug(UV_DEBUG_TRANSFILE, UV_DEBUG_WARN, "invalid transaction index");
+				index_invalidate(notify.tf);
 			}
 		}
 	}