diff --git a/src/CelerisLab/lbm/blocks.py b/src/CelerisLab/lbm/blocks.py
index 3b7ac30..4fc9975 100644
--- a/src/CelerisLab/lbm/blocks.py
+++ b/src/CelerisLab/lbm/blocks.py
@@ -1,3 +1,4 @@
+# CelerisLab/lbm/blocks.py
 """CPU layout for fixed-size 2D blocks: core ownership, halo pairs and packing.
 
 Dense arrays are Q-major (q, y, x) with cell y*nx+x, as in core/layout.cuh.