From aa3f869798037bf2fde251deacf66936db379c5a Mon Sep 17 00:00:00 2001
From: Alex Shinn <alexshinn@gmail.com>
Date: Tue, 14 Apr 2015 23:22:48 +0900
Subject: [PATCH] Avoiding potential segfault from trying to capture temporary
 local variables in a macro. Fixes issue #252.

---
 eval.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/eval.c b/eval.c
index 41fa97ba..d195eb6c 100644
--- a/eval.c
+++ b/eval.c
@@ -100,7 +100,7 @@ static sexp sexp_env_cell_loc1 (sexp env, sexp key, int localp, sexp *varenv) {
 
 static sexp sexp_env_cell_loc (sexp ctx, sexp env, sexp key, int localp, sexp *varenv) {
   sexp cell = sexp_env_cell_loc1(env, key, localp, varenv);
-  while (!cell && sexp_synclop(key)) {
+  while (!cell && key && sexp_synclop(key)) {
     if (sexp_not(sexp_memq(ctx, sexp_synclo_expr(key), sexp_context_fv(ctx)))
         && sexp_not(sexp_memq(ctx, sexp_synclo_expr(key), sexp_synclo_free_vars(key))))
       env = sexp_synclo_env(key);