diff --git a/src/system_wrappers/interface/sleep.h b/src/system_wrappers/interface/sleep.h
index 735efefcc..c0205bf08 100644
--- a/src/system_wrappers/interface/sleep.h
+++ b/src/system_wrappers/interface/sleep.h
@@ -9,6 +9,9 @@
  */
 // An OS-independent sleep function.
 
+#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_SLEEP_H_
+#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_SLEEP_H_
+
 namespace webrtc {
 
 // This function sleeps for the specified number of milliseconds.
@@ -17,3 +20,5 @@ namespace webrtc {
 void SleepMs(int msecs);
 
 }  // namespace webrtc
+
+#endif  // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_SLEEP_H_