diff --git a/Xext/xtest.c b/Xext/xtest.c
index f03d8c951..012e328a0 100644
--- a/Xext/xtest.c
+++ b/Xext/xtest.c
@@ -346,6 +346,10 @@ ProcXTestFakeInput(ClientPtr client)
             return BadAccess;
 
         dev = GetXTestDevice(dev);
+
+        /* This can only happen if we passed a slave to GetXTestDevice() */
+        if (!dev)
+            return BadAccess;
     }