diff --git a/lib/libc/tests/stdlib/dynthr_mod/dynthr_mod.c b/lib/libc/tests/stdlib/dynthr_mod/dynthr_mod.c
index 4f5622f47a8..c19a1a54a8b 100644
--- a/lib/libc/tests/stdlib/dynthr_mod/dynthr_mod.c
+++ b/lib/libc/tests/stdlib/dynthr_mod/dynthr_mod.c
@@ -51,6 +51,7 @@ mod_thread(void *ptr __unused)
 	char *volatile dummy;
 
 	dummy = malloc(500);
+	*dummy = 'a';
 	return (NULL);
 }