diff --git a/relaxng.c b/relaxng.c
index 1ba4fba..4273db3 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -1095,7 +1095,7 @@
 {
     int i;
 
-    if (state == NULL) {
+    if (state == NULL || states == NULL) {
         return (-1);
     }
     if (states->nbState >= states->maxState) {