diff --git a/awkgram.y b/awkgram.y
index b72d1c8..9bd3916 100644
--- a/awkgram.y
+++ b/awkgram.y
@@ -1607,7 +1607,7 @@ common_exp
 			$$ = $1;
 		} else {
 	plain_concat:
-			$$ = list_append(list_merge($1, $2), instruction(Op_concat));
+			$$ = list_append(list_merge($1, $2), bcalloc(Op_concat, 1, sourceline));
 			$$->lasti->concat_flag = (is_simple_var ? CSVAR : 0);
 			$$->lasti->expr_count = count;
 			if (count > max_args)