diff --git a/gfx/thebes/gfxFont-Impl.h b/gfx/thebes/gfxFont-Impl.h
index 0dd84a882b..2661d1f40a 100644
--- a/gfx/thebes/gfxFont-Impl.h
+++ b/gfx/thebes/gfxFont-Impl.h
@@ -6,6 +6,9 @@
 #ifndef GFX_FONT_IMPL_H
 #define GFX_FONT_IMPL_H
 
+#include "mozilla/DebugOnly.h"
+using mozilla::DebugOnly;
+
 #ifdef __GNUC__
 #define GFX_MAYBE_UNUSED __attribute__((unused))
 #else