diff --git a/Xi/xiselectev.c b/Xi/xiselectev.c
index 6734da991..98b591901 100644
--- a/Xi/xiselectev.c
+++ b/Xi/xiselectev.c
@@ -108,10 +108,10 @@ ProcXISelectEvent(ClientPtr client)
                 return BadValue;
         }
 
-        if ((evmask->mask_len * 4) > XI_LASTEVENT)
+        if ((evmask->mask_len * 4) >= (XI_LASTEVENT + 8)/8)
         {
             unsigned char *bits = (unsigned char*)&evmask[1];
-            for (i = XI_LASTEVENT; i < evmask->mask_len * 4; i++)
+            for (i = XI_LASTEVENT + 1; i < evmask->mask_len * 4; i++)
             {
                 if (BitIsOn(bits, i))
                     return BadValue;