diff --git a/av1/common/onyxc_int.h b/av1/common/onyxc_int.h
index e114848..3c31ab2 100644
--- a/av1/common/onyxc_int.h
+++ b/av1/common/onyxc_int.h
@@ -252,6 +252,7 @@
 
   int largest_tile_id;
   size_t largest_tile_size;
+  int context_update_tile_id;
 
   // Scale of the current frame with respect to itself.
   struct scale_factors sf_identity;
diff --git a/av1/common/tile_common.c b/av1/common/tile_common.c
index 01766b0..bf9562c 100644
--- a/av1/common/tile_common.c
+++ b/av1/common/tile_common.c
@@ -42,8 +42,6 @@
   cm->max_log2_tile_rows = tile_log2(1, AOMMIN(sb_rows, MAX_TILE_ROWS));
   cm->min_log2_tiles = tile_log2(max_tile_area_sb, sb_cols * sb_rows);
   cm->min_log2_tiles = AOMMAX(cm->min_log2_tiles, cm->min_log2_tile_cols);
-  // TODO(dominic.symes@arm.com):
-  // Add in levelMinLog2Tiles as a lower limit when levels are defined
 }
 
 void av1_calculate_tile_cols(AV1_COMMON *const cm) {
diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 3a9749f..a8652d3 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -1580,7 +1580,11 @@
 
   read_tile_info_max_tile(cm, rb);
 
+  cm->context_update_tile_id = 0;
   if (cm->tile_rows * cm->tile_cols > 1) {
+    // tile to use for cdf update
+    cm->context_update_tile_id =
+        aom_rb_read_literal(rb, cm->log2_tile_rows + cm->log2_tile_cols);
     // tile size magnitude
     pbi->tile_size_bytes = aom_rb_read_literal(rb, 2) + 1;
   }
@@ -1771,11 +1775,6 @@
   int tc = 0;
   int first_tile_in_tg = 0;
 
-  if (startTile == 0) {
-    cm->largest_tile_size = 0;
-    cm->largest_tile_id = 0;
-  }
-
   for (int r = 0; r < tile_rows; ++r) {
     for (int c = 0; c < tile_cols; ++c, ++tc) {
       TileBufferDec *const buf = &tile_buffers[r][c];
@@ -1793,10 +1792,6 @@
       data += hdr_offset;
       get_tile_buffer(data_end, pbi->tile_size_bytes, is_last,
                       &pbi->common.error, &data, buf);
-      if (buf->size > cm->largest_tile_size) {
-        cm->largest_tile_size = buf->size;
-        cm->largest_tile_id = r * tile_cols + c;
-      }
     }
   }
 }
@@ -3270,7 +3265,7 @@
 
   if (!xd->corrupted) {
     if (cm->refresh_frame_context == REFRESH_FRAME_CONTEXT_BACKWARD) {
-      *cm->fc = pbi->tile_data[cm->largest_tile_id].tctx;
+      *cm->fc = pbi->tile_data[cm->context_update_tile_id].tctx;
       av1_reset_cdf_symbol_counters(cm->fc);
     } else {
       debug_check_frame_counts(cm);
diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 126a5c3..7c59568 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -2215,6 +2215,8 @@
     return;
   }
   if (cm->tile_rows * cm->tile_cols > 1) {
+    // tile id used for cdf update
+    aom_wb_write_literal(wb, 0, cm->log2_tile_cols + cm->log2_tile_rows);
     // Number of bytes in tile size - 1
     aom_wb_write_literal(wb, 3, 2);
   }
@@ -3681,6 +3683,11 @@
                              max_tile_col_size, &tile_size_bytes, &unused);
     total_size += tile_data_offset;
     assert(tile_size_bytes >= 1 && tile_size_bytes <= 4);
+
+    // fill in id of tile to use for the cdf update which encoder currently
+    // sets to the largest tile (but is up to the encoder)
+    aom_wb_overwrite_literal(saved_wb, cm->largest_tile_id,
+                             cm->log2_tile_cols + cm->log2_tile_rows);
     aom_wb_overwrite_literal(saved_wb, tile_size_bytes - 1, 2);
 
     // Update the OBU length if remux_tiles() reduced the size.