diff --git a/test/xi2/protocol-xiselectevents.c b/test/xi2/protocol-xiselectevents.c
index 825eeb628..ac38c53c9 100644
--- a/test/xi2/protocol-xiselectevents.c
+++ b/test/xi2/protocol-xiselectevents.c
@@ -95,7 +95,14 @@ static void request_XISelectEvent(xXISelectEventsReq *req, int error)
     ClientRec client;
     xXIEventMask *mask, *next;
 
-    req->length = (sz_xXISelectEventsReq/4) + req->num_masks;
+    req->length = (sz_xXISelectEventsReq/4);
+    mask = (xXIEventMask*)&req[1];
+    for (i = 0; i < req->num_masks; i++)
+    {
+        req->length += sizeof(xXIEventMask)/4 + mask->mask_len;
+        mask = (xXIEventMask*)((char*)&mask[1] + mask->mask_len * 4);
+    }
+
     client = init_client(req->length, req);
 
     rc = ProcXISelectEvents(&client);
@@ -280,16 +287,24 @@ static void test_XISelectEvents(void)
     req->num_masks = 0xFFFF;
     request_XISelectEvent(req, BadLength);
 
-    /* testing various device ids */
     req->win = ROOT_WINDOW_ID;
     req->num_masks = 1;
 
+    g_test_message("Triggering bogus mask length error");
+    mask = (xXIEventMask*)&req[1];
+    mask->deviceid = 0;
+    mask->mask_len = 0xFFFF;
+    request_XISelectEvent(req, BadLength);
+
+    /* testing various device ids */
     g_test_message("Testing existing device ids.");
     for (i = 0; i < 6; i++)
     {
         mask = (xXIEventMask*)&req[1];
         mask->deviceid = i;
         mask->mask_len = 1;
+        req->win = ROOT_WINDOW_ID;
+        req->num_masks = 1;
         request_XISelectEvent(req, Success);
     }