diff --git a/mozilla/widget/src/os2/nsClipboard.cpp b/mozilla/widget/src/os2/nsClipboard.cpp
index 3521fe78ff4..1ef21f034c6 100644
--- a/mozilla/widget/src/os2/nsClipboard.cpp
+++ b/mozilla/widget/src/os2/nsClipboard.cpp
@@ -30,6 +30,7 @@
 #include "nsPrimitiveHelpers.h"
 #include "nsXPIDLString.h"
 #include "prmem.h"
+#include "nsIObserverService.h"
 
 #include "nsOS2Uni.h"