diff --git a/gfx/layers/opengl/ThebesLayerOGL.cpp b/gfx/layers/opengl/ThebesLayerOGL.cpp
index deb77c94a1f..7be49644480 100644
--- a/gfx/layers/opengl/ThebesLayerOGL.cpp
+++ b/gfx/layers/opengl/ThebesLayerOGL.cpp
@@ -78,6 +78,7 @@ ThebesLayerOGL::ThebesLayerOGL(LayerManagerOGL *aManager)
   , LayerOGL(aManager)
   , mTexture(0)
   , mOffscreenFormat(gfxASurface::ImageFormatUnknown)
+  , mOffscreenSize(-1,-1)
 {
   mImplData = static_cast<LayerOGL*>(this);
 }