--- a/mozglue/misc/TimeStamp.h
+++ b/mozglue/misc/TimeStamp.h
@@ -586,16 +586,17 @@ public:
   // two TimeStamps, or scaling TimeStamps, is nonsense and must never
   // be allowed.
 
   static MFBT_API void Startup();
   static MFBT_API void Shutdown();
 
 private:
   friend struct IPC::ParamTraits<mozilla::TimeStamp>;
+  friend void StartupTimelineRecordExternal(int, uint64_t);
 
   MOZ_IMPLICIT TimeStamp(TimeStampValue aValue) : mValue(aValue) {}
 
   static MFBT_API TimeStamp Now(bool aHighResolution);
 
   /**
    * Computes the uptime of the current process in microseconds. The result
    * is platform-dependent and needs to be checked against existing timestamps

--- a/mozglue/misc/TimeStamp_windows.h
+++ b/mozglue/misc/TimeStamp_windows.h
@@ -12,16 +12,17 @@
 namespace mozilla {
 
 class TimeStamp;
 
 class TimeStampValue
 {
   friend struct IPC::ParamTraits<mozilla::TimeStampValue>;
   friend class TimeStamp;
+  friend void StartupTimelineRecordExternal(int, uint64_t);
 
   // Both QPC and GTC are kept in [mt] units.
   uint64_t mGTC;
   uint64_t mQPC;
   bool mHasQPC;
   bool mIsNull;
 
   MFBT_API TimeStampValue(uint64_t aGTC, uint64_t aQPC, bool aHasQPC);