diff --git a/gfx/thebes/gfxWindowsPlatform.cpp b/gfx/thebes/gfxWindowsPlatform.cpp
index 4cc3b174e776..94d8321d150e 100644
--- a/gfx/thebes/gfxWindowsPlatform.cpp
+++ b/gfx/thebes/gfxWindowsPlatform.cpp
@@ -506,7 +506,7 @@ gfxWindowsPlatform::UpdateRenderMode()
 #endif
 
     uint32_t canvasMask = 1 << BACKEND_CAIRO;
-    uint32_t contentMask = 0;
+    uint32_t contentMask = 1 << BACKEND_CAIRO;
     if (mRenderMode == RENDER_DIRECT2D) {
       canvasMask |= 1 << BACKEND_DIRECT2D;
       contentMask |= 1 << BACKEND_DIRECT2D;