diff --git a/GL/glx/glxglcore.c b/GL/glx/glxglcore.c
index 1eac0eb3e..c8a2514d2 100644
--- a/GL/glx/glxglcore.c
+++ b/GL/glx/glxglcore.c
@@ -432,6 +432,7 @@ __glXMesaScreenProbe(ScreenPtr pScreen)
     screen->base.destroy        = __glXMesaScreenDestroy;
     screen->base.createContext  = __glXMesaScreenCreateContext;
     screen->base.createDrawable = __glXMesaScreenCreateDrawable;
+    screen->base.swapInterval  = NULL;
     screen->base.pScreen       = pScreen;
 
     return &screen->base;