diff --git a/test/zdtm/lib/msg.c b/test/zdtm/lib/msg.c
index 17a298e43..8a80ae224 100644
--- a/test/zdtm/lib/msg.c
+++ b/test/zdtm/lib/msg.c
@@ -56,5 +56,5 @@ void test_msg(const char *format, ...)
 	off += vsnprintf(buf + off, sizeof(buf) - off, format, arg);
 	va_end(arg);
 
-	fprintf(stderr, buf);
+	fprintf(stderr, "%s", buf);
 }