diff --git a/mozilla/base/public/nsAutoLock.h b/mozilla/base/public/nsAutoLock.h
index cee5790e893..8c52072639f 100644
--- a/mozilla/base/public/nsAutoLock.h
+++ b/mozilla/base/public/nsAutoLock.h
@@ -126,6 +126,7 @@ public:
 //    }
 
 #include "prcmon.h"
+#include "nsError.h"
 
 class nsAutoMonitor {
 public:
diff --git a/mozilla/xpcom/threads/nsAutoLock.h b/mozilla/xpcom/threads/nsAutoLock.h
index cee5790e893..8c52072639f 100644
--- a/mozilla/xpcom/threads/nsAutoLock.h
+++ b/mozilla/xpcom/threads/nsAutoLock.h
@@ -126,6 +126,7 @@ public:
 //    }
 
 #include "prcmon.h"
+#include "nsError.h"
 
 class nsAutoMonitor {
 public: