diff --git a/lib/isc/buffer.c b/lib/isc/buffer.c
index 219a5493ab..66defe8bbb 100644
--- a/lib/isc/buffer.c
+++ b/lib/isc/buffer.c
@@ -550,10 +550,11 @@ isc_buffer_allocate(isc_mem_t *mctx, isc_buffer_t **dynbuffer,
 	bdata = isc_mem_get(mctx, length);
 
 	isc_buffer_init(dbuf, bdata, length);
-	dbuf->mctx = mctx;
 
 	ENSURE(ISC_BUFFER_VALID(dbuf));
 
+	dbuf->mctx = mctx;
+
 	*dynbuffer = dbuf;
 
 	return (ISC_R_SUCCESS);