diff --git a/kuser/klist.c b/kuser/klist.c
index 46d918849..4640a016b 100644
--- a/kuser/klist.c
+++ b/kuser/klist.c
@@ -360,7 +360,8 @@ check_expiration(krb5_context context,
     if (ret || t == 0)
 	return 1;
 
-    *expiration = time(NULL) + t;
+    if (expiration)
+	*expiration = time(NULL) + t;
 
     return 0;
 }