diff --git a/src/x509.c b/src/x509.c
index 5e7a1dd..36406b8 100644
--- a/src/x509.c
+++ b/src/x509.c
@@ -86,7 +86,7 @@ static void push_asn1_objname(lua_State* L, ASN1_OBJECT *object, int no_name)
  */
 static void push_asn1_string(lua_State* L, ASN1_STRING *string, int encode)
 {
-  size_t len;
+  int len;
   unsigned char *data;
   if (!string)
     lua_pushnil(L);