diff --git a/deploy/nixos/README.md b/deploy/nixos/README.md
index 121a69c..250913d 100644
--- a/deploy/nixos/README.md
+++ b/deploy/nixos/README.md
@@ -88,9 +88,10 @@ The bitSpire-flashed USB will show up as another disk (`sdb` or similar) — not
 ### 4. dd the bitSpire image to the eMMC
 
 ```sh
-# Limit count to ~8.8 GB (the actual image size + small margin) to avoid
-# spending 30 minutes copying empty USB tail
-dd if=/dev/sdb of=/dev/mmcblk0 bs=4M count=2200 status=progress conv=fsync && sync
+# Limit count to ~11.2 GB (the actual image size + small margin) to avoid
+# spending 30 minutes copying empty USB tail. Bump this count if the
+# image grows further on future nixpkgs bumps — check `ls -lh result/`.
+dd if=/dev/sdb of=/dev/mmcblk0 bs=4M count=2800 status=progress conv=fsync && sync
 ```
 
 ### 5. Repair the GPT secondary header