diff --git a/shader_deblocking/README.md b/shader_deblocking/README.md
index 87ccdc0..64b1886 100644
--- a/shader_deblocking/README.md
+++ b/shader_deblocking/README.md
@@ -73,6 +73,8 @@ Many variations and optimizations of this basic idea are possible.
 
 This screenshot shows how the pixel shader computes texture block boundaries in effective mipmap space. To see this visualization, press '1' to enable deblocking, then '2' to enable block edge visualization. Only white areas in this visualization are modified by this shader, leaving the inner block texels unmodified.
 
+Obviously, it's crucial that the block size passed into the shader via constants exactly matches the ASTC texture's block size.
+
 ---
 
 ## Usage and Controls