diff --git a/adb_utils.h b/adb_utils.h
index 16317e0..2b59034 100644
--- a/adb_utils.h
+++ b/adb_utils.h
@@ -21,6 +21,8 @@
 
 #include <android-base/macros.h>
 
+int usage(const char*, ...);
+
 void close_stdin();
 
 bool getcwd(std::string* cwd);