--- a/glx/glxdri.c	
+++ a/glx/glxdri.c	
@@ -978,6 +978,8 @@ __glXDRIscreenProbe(ScreenPtr pScreen)
         return NULL;
     }
 
+    framebuffer.base = NULL;
+
     screen = calloc(1, sizeof *screen);
     if (screen == NULL)
         return NULL;