diff --git a/src/lib/openjp2/t2.c b/src/lib/openjp2/t2.c
index 0982d6b5..6aee8c72 100644
--- a/src/lib/openjp2/t2.c
+++ b/src/lib/openjp2/t2.c
@@ -441,7 +441,8 @@ OPJ_BOOL opj_t2_decode_packets( opj_t2_t *p_t2,
 
         /* don't forget to release pi */
         opj_pi_destroy(l_pi,l_nb_pocs);
-        *p_data_read = l_current_data - p_src;
+        assert( l_current_data - p_src <  UINT32_MAX );
+        *p_data_read = (OPJ_UINT32)(l_current_data - p_src);
         return OPJ_TRUE;
 }