diff --git a/tools/syz-usbgen/keyboard.c b/tools/syz-usbgen/keyboard.c
index 9456189c..2a6015d4 100644
--- a/tools/syz-usbgen/keyboard.c
+++ b/tools/syz-usbgen/keyboard.c
@@ -1,3 +1,5 @@
+// +build
+
 // Copyright 2019 syzkaller project authors. All rights reserved.
 // Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.