diff --git a/dom/ipc/PreallocatedProcessManager.cpp b/dom/ipc/PreallocatedProcessManager.cpp
index 81294e6d561e..c079e9e75bcc 100644
--- a/dom/ipc/PreallocatedProcessManager.cpp
+++ b/dom/ipc/PreallocatedProcessManager.cpp
@@ -7,6 +7,7 @@
 #include "mozilla/PreallocatedProcessManager.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/unused.h"
 #include "mozilla/dom/ContentParent.h"
 #include "mozilla/dom/ScriptSettings.h"
 #include "nsIPropertyBag2.h"