diff --git a/dlls/wined3d/ati_fragment_shader.c b/dlls/wined3d/ati_fragment_shader.c
index 6aa91a6748f..4994d96a335 100644
--- a/dlls/wined3d/ati_fragment_shader.c
+++ b/dlls/wined3d/ati_fragment_shader.c
@@ -157,6 +157,7 @@ static const char *debug_rep(GLuint rep) {
         case GL_RED:                    return "GL_RED";
         case GL_GREEN:                  return "GL_GREEN";
         case GL_BLUE:                   return "GL_BLUE";
+        case GL_ALPHA:                  return "GL_ALPHA";
         default:                        return "unknown argrep";
     }
 }