diff --git a/Xext/xtest.c b/Xext/xtest.c
index 5f4d6eadbb..332bc197a1 100644
--- a/Xext/xtest.c
+++ b/Xext/xtest.c
@@ -355,6 +355,10 @@ ProcXTestFakeInput(ClientPtr client)
             return BadAccess;
 
         dev = GetXTestDevice(dev);
+
+        /* This can only happen if we passed a slave to GetXTestDevice() */
+        if (!dev)
+            return BadAccess;
     }