diff --git a/Xi/querydp.c b/Xi/querydp.c
index bc6feb1b1..e5bf98d86 100644
--- a/Xi/querydp.c
+++ b/Xi/querydp.c
@@ -132,7 +132,7 @@ ProcXIQueryPointer(ClientPtr client)
     if (pDev->button)
     {
         int i, down;
-        rep.buttons_len = ((pDev->button->numButtons/8) + 3)/4;
+        rep.buttons_len = (((pDev->button->numButtons + 7)/8) + 3)/4;
         rep.length += rep.buttons_len;
         buttons = xcalloc(rep.buttons_len, 4);
         if (!buttons)