diff --git a/cogl-gst/cogl-gst-video-sink.c b/cogl-gst/cogl-gst-video-sink.c
index 9a811b20e..acfaa77a6 100644
--- a/cogl-gst/cogl-gst-video-sink.c
+++ b/cogl-gst/cogl-gst-video-sink.c
@@ -718,9 +718,9 @@ cogl_gst_yv12_glsl_setup_pipeline (CoglGstVideoSink *sink,
                          "cogl_gst_sample_video%i (vec2 UV)\n"
                          "{\n"
                          "  float y = 1.1640625 * "
-                         "(texture2D (cogl_sampler%i, UV).g - 0.0625);\n"
-                         "  float u = texture2D (cogl_sampler%i, UV).g - 0.5;\n"
-                         "  float v = texture2D (cogl_sampler%i, UV).g - 0.5;\n"
+                         "(texture2D (cogl_sampler%i, UV).a - 0.0625);\n"
+                         "  float u = texture2D (cogl_sampler%i, UV).a - 0.5;\n"
+                         "  float v = texture2D (cogl_sampler%i, UV).a - 0.5;\n"
                          "  vec4 color;\n"
                          "  color.r = y + 1.59765625 * v;\n"
                          "  color.g = y - 0.390625 * u - 0.8125 * v;\n"