diff --git a/Xext/xvdisp.c b/Xext/xvdisp.c
index 03fdafc9f0..243a0fddbf 100644
--- a/Xext/xvdisp.c
+++ b/Xext/xvdisp.c
@@ -765,6 +765,7 @@ ProcXvQueryImageAttributes(ClientPtr client)
 
     /* allocating for `offsets` as well as `pitches` in one block */
     /* both having CARD32 * num_planes (actually int32_t put into CARD32) */
+    __size_assert(int, sizeof(INT32));
     int *offsets = x_rpcbuf_reserve(&rpcbuf, 2 * num_planes * sizeof(int));
     if (!offsets)
         return BadAlloc;