--- a/gfx/gl/GLReadTexImageHelper.cpp
+++ b/gfx/gl/GLReadTexImageHelper.cpp
@@ -412,16 +412,17 @@ ReadPixelsIntoDataSurface(GLContext* gl,
         gfx::Factory::CopyDataSourceSurface(readSurf, dest);
     }
 
     // Check if GL is giving back 1.0 alpha for
     // RGBA reads to RGBA images from no-alpha buffers.
 #ifdef XP_MACOSX
     if (gl->WorkAroundDriverBugs() &&
         gl->Vendor() == gl::GLVendor::NVIDIA &&
+        !gl->IsCoreProfile() &&
         hasAlpha &&
         width && height)
     {
         GLint alphaBits = 0;
         gl->fGetIntegerv(LOCAL_GL_ALPHA_BITS, &alphaBits);
         if (!alphaBits) {
             const uint32_t alphaMask = gfxPackedPixelNoPreMultiply(0xff,0,0,0);