diff --git a/hw/xfree86/modes/xf86Crtc.h b/hw/xfree86/modes/xf86Crtc.h
index fcba5c902..7a562874c 100644
--- a/hw/xfree86/modes/xf86Crtc.h
+++ b/hw/xfree86/modes/xf86Crtc.h
@@ -839,6 +839,9 @@ xf86CompatOutput(ScrnInfoPtr pScrn)
 {
     xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(pScrn);
 
+    if (xf86CrtcConfigPrivateIndex == -1)
+        return NULL;
+
     if (config->compat_output < 0)
         return NULL;
     return config->output[config->compat_output];