diff --git a/lldb/tools/debugserver/source/MacOSX/MachThread.h b/lldb/tools/debugserver/source/MacOSX/MachThread.h
index 1086b7c986f1..69567425542f 100644
--- a/lldb/tools/debugserver/source/MacOSX/MachThread.h
+++ b/lldb/tools/debugserver/source/MacOSX/MachThread.h
@@ -13,6 +13,7 @@
 #ifndef LLDB_TOOLS_DEBUGSERVER_SOURCE_MACOSX_MACHTHREAD_H
 #define LLDB_TOOLS_DEBUGSERVER_SOURCE_MACOSX_MACHTHREAD_H
 
+#include <mutex>
 #include <string>
 #include <vector>