diff --git a/src/gallium/drivers/radeonsi/radeon_vcn_dec.c b/src/gallium/drivers/radeonsi/radeon_vcn_dec.c
index b7aed7a9b7e..7570a7f036b 100644
--- a/src/gallium/drivers/radeonsi/radeon_vcn_dec.c
+++ b/src/gallium/drivers/radeonsi/radeon_vcn_dec.c
@@ -1793,15 +1793,22 @@ static struct pb_buffer_lean *rvcn_dec_message_decode(struct radeon_decoder *dec
          return NULL;
       }
       int ss_length = MIN2(secure_buf->desc.subsamples_length, MAX_SUBSAMPLES);
+      int total_ss_size = 0;
       uint32_t *ss_ptr = dec->ws->buffer_map(dec->ws, dec->subsample.res->buf, &dec->cs,
                                              PIPE_MAP_WRITE | RADEON_MAP_TEMPORARY);
       if (!ss_ptr) {
          RADEON_DEC_ERR("Failed to map subsample buffer memory.\n");
          return NULL;
       }
-      for (int i = 0; i < ss_length; i++)
+      for (int i = 0; i < ss_length; i++) {
          memcpy(&ss_ptr[i * 2], &secure_buf->desc.subsamples[i].num_bytes_clear, 8);
-      ss_ptr[ss_length * 2 - 1] = align(ss_ptr[ss_length * 2 - 1], 256);
+         total_ss_size += ss_ptr[i * 2] + ss_ptr[i * 2 + 1];
+      }
+      assert(total_ss_size <= decode->bsd_size);
+      if (ss_ptr[ss_length * 2 - 1] != 0)
+         ss_ptr[ss_length * 2 - 1] += (decode->bsd_size - total_ss_size);
+      else
+         ss_ptr[ss_length * 2 - 2] += (decode->bsd_size - total_ss_size);
       dec->ws->buffer_unmap(dec->ws, dec->subsample.res->buf);
    }