--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -465,12 +465,12 @@ replace_stringInfo(StringInfo string, const char *replace, const char *replaceme

        while ((ptr = strstr(string->data, replace)) != NULL)
        {
-               char       *dup = pg_strdup(string->data);
+               char       *suffix = pnstrdup(ptr + strlen(replace), string->maxlen);
                size_t          pos = ptr - string->data;

                string->len = pos;
                appendStringInfoString(string, replacement);
-               appendStringInfoString(string, dup + pos + strlen(replace));
+               appendStringInfoString(string, suffix);

-               free(dup);
+               free(suffix);
        }