Index: intern/ghost/intern/GHOST_WindowX11.cpp
===================================================================
--- intern/ghost/intern/GHOST_WindowX11.cpp    (revision 21471)
+++ intern/ghost/intern/GHOST_WindowX11.cpp    (working copy)
@@ -167,6 +167,7 @@
     attributes[i++] = GLX_RED_SIZE;   attributes[i++] = 1;
     attributes[i++] = GLX_BLUE_SIZE;  attributes[i++] = 1;
     attributes[i++] = GLX_GREEN_SIZE; attributes[i++] = 1;
+    attributes[i++] = GLX_ALPHA_SIZE; attributes[i++] = 1;
     attributes[i++] = GLX_DEPTH_SIZE; attributes[i++] = 1;
     attributes[i] = None;