diff --git a/parser.c b/parser.c
index acbba21..170e332 100644
--- a/parser.c
+++ b/parser.c
@@ -209,6 +209,10 @@ static sy_elem syop(const oper_info *op) {
 
 static bool parser_sy_pop(parser_t *parser, shynt *sy)
 {
+    if (!sy->ops_count) {
+        parseerror(parser, "internal error: missing operator");
+        return false;
+    }
     return true;
 }