diff --git a/tests/tgen-mstring.c b/tests/tgen-mstring.c
index 02c9863d..b450290b 100644
--- a/tests/tgen-mstring.c
+++ b/tests/tgen-mstring.c
@@ -32,3 +32,8 @@ void convert(string_t s, unsigned n)
 {
   m_string_set_ui(s, n);
 }
+
+void construct(char s[], unsigned n)
+{
+  strcpy(s, M_CSTR("Hello %u worlds"));
+}