diff --git a/spec/basis_spec.txt b/spec/basis_spec.txt
index ffb5a05..ba041a3 100644
--- a/spec/basis_spec.txt
+++ b/spec/basis_spec.txt
@@ -818,7 +818,7 @@
         
     // For texture video, remember the endpoint and selector indices used by the block on this frame, for later reuse on the next frame.
     if (is_video)
-        prev_frame_indices[block_x + block_y * num_blocks_x] = endpoint_index | (selector_index << 16);
+        prev_frame_indices[block_x][block_y] = endpoint_index | (selector_index << 16);
 
     // The block is fully decoded here. The codebook indices are endpoint_index and selector_index.
     // Make sure they are valid