diff --git a/ivlpp/lexor.lex b/ivlpp/lexor.lex
index 9094368ac..b20d27119 100644
--- a/ivlpp/lexor.lex
+++ b/ivlpp/lexor.lex
@@ -1599,10 +1599,10 @@ static void macro_start_args(void)
      * entry for arg 0. This will be used by macro_finish_arg() to
      * calculate the buffer location for arg 1.
      */
-    if (def_buf) {
-      def_buf_free = def_buf_size - 1;
-      def_buf[0] = 0;
-    }
+    def_buf_grow_to_fit(1);
+    def_buf_free = def_buf_size - 1;
+    def_buf[0] = 0;
+
     def_argo[0] = 0;
     def_argl[0] = 0;
     def_argc = 1;