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-rw-r--r--widget/windows/nsWindowGfx.cpp2
1 files changed, 2 insertions, 0 deletions
diff --git a/widget/windows/nsWindowGfx.cpp b/widget/windows/nsWindowGfx.cpp
index a88631f89..9b303a0f2 100644
--- a/widget/windows/nsWindowGfx.cpp
+++ b/widget/windows/nsWindowGfx.cpp
@@ -320,6 +320,8 @@ bool nsWindow::OnPaint(HDC aDC, uint32_t aNestingLevel)
#if defined(MOZ_XUL)
// don't support transparency for non-GDI rendering, for now
if (eTransparencyTransparent == mTransparencyMode) {
+ // This mutex needs to be held when EnsureTransparentSurface is called.
+ MutexAutoLock lock(mBasicLayersSurface->GetTransparentSurfaceLock());
targetSurface = mBasicLayersSurface->EnsureTransparentSurface();
}
#endif