diff --git a/README.md b/README.md
index f2c3ff8..2a3e8b6 100644
--- a/README.md
+++ b/README.md
@@ -79,7 +79,7 @@ sudo apt install wimtools dosfstools gdisk mtools p7zip-full
 ./build-windows-install-disk.sh [--force] install-iso/Windows11_..._arm64_....iso
 ```
 
-The output defaults to the ISO path with `.install.img` in place of `.iso`. The
+The output defaults to the ISO path with `.img` in place of `.iso`. The
 image is built without root. The ISO has to be read as UDF (its ISO 9660 side only
 holds a README): macOS uses `hdiutil`, Linux uses `mount -t udf` as root,
 otherwise `udisksctl`, otherwise `7z` extracts it into a temporary directory
diff --git a/build-windows-install-disk.sh b/build-windows-install-disk.sh
index 6cbdee5..3660642 100755
--- a/build-windows-install-disk.sh
+++ b/build-windows-install-disk.sh
@@ -18,7 +18,7 @@
 #   Debian            wimtools dosfstools gdisk mtools udisks2
 #
 # Usage: build-windows-install-disk.sh [--force] ISO [OUTPUT.img]
-# OUTPUT defaults to the ISO path with ".install.img" in place of ".iso".
+# OUTPUT defaults to the ISO path with ".img" in place of ".iso".
 set -euo pipefail
 
 usage() {
@@ -39,7 +39,7 @@ if ((${#args[@]} < 1 || ${#args[@]} > 2)); then
   exit 2
 fi
 iso="${args[0]}"
-output="${args[1]:-${iso%.*}.install.img}"
+output="${args[1]:-${iso%.*}.img}"
 
 die() {
   printf 'Error: %s\n' "$1" >&2