diff --git a/crypto/stack/stack.c b/crypto/stack/stack.c
index c584515..e893221 100644
--- a/crypto/stack/stack.c
+++ b/crypto/stack/stack.c
@@ -329,7 +329,7 @@
 void sk_sort(_STACK *sk) {
   int (*comp_func)(const void *,const void *);
 
-  if (sk == NULL || sk->sorted) {
+  if (sk == NULL || sk->comp == NULL || sk->sorted) {
     return;
   }