diff --git a/lib/sxmplv2.c b/lib/sxmplv2.c
index cf76126..67bd9db 100644
--- a/lib/sxmplv2.c
+++ b/lib/sxmplv2.c
@@ -513,7 +513,7 @@ static int __eval_sysrpc(sxlink_t *link, sexp_t *sx, int builtin)
   if(builtin) rpc_list = link->hub->stream_rpc;
   else rpc_list = link->hub->system_rpc;
 
-  if(sx->ty == SEXP_LIST)    rpcf = sx->list->val;
+  if(sx->ty == SEXP_LIST && sx->list != NULL)    rpcf = sx->list->val;
   else return SXE_BADPROTO;
 
   /* find an appropriate function */