diff --git a/src/lib/openjp2/ht_dec.c b/src/lib/openjp2/ht_dec.c
index 62a6c9e1..186ae24c 100644
--- a/src/lib/openjp2/ht_dec.c
+++ b/src/lib/openjp2/ht_dec.c
@@ -1192,6 +1192,7 @@ OPJ_BOOL opj_t1_ht_decode_cblk(opj_t1_t *t1,
         cblkdata = t1->cblkdatabuffer;
         cblk_len = 0;
         for (i = 0; i < cblk->numchunks; i++) {
+            assert(cblkdata!=NULL && "memcpy on NULL is undefined behaviour");
             memcpy(cblkdata + cblk_len, cblk->chunks[i].data, cblk->chunks[i].len);
             cblk_len += cblk->chunks[i].len;
         }