diff --git a/docs/site/getting-started/installer.md b/docs/site/getting-started/installer.md
index 591aec74f..797e6fec5 100644
--- a/docs/site/getting-started/installer.md
+++ b/docs/site/getting-started/installer.md
@@ -49,7 +49,7 @@ sudo umount /dev/sdb1
     clan flash --flake git+https://git.clan.lol/clan/clan-core \
       --ssh-pubkey $HOME/.ssh/id_ed25519.pub \
       --keymap us \
-      --language en_US.utf-8 \
+      --language en_US.UTF-8 \
       --disk main /dev/sd<X> \
       flash-installer
     ```
diff --git a/pkgs/clan-cli/tests/test_deserializers.py b/pkgs/clan-cli/tests/test_deserializers.py
index 3fea9798e..b475c00b9 100644
--- a/pkgs/clan-cli/tests/test_deserializers.py
+++ b/pkgs/clan-cli/tests/test_deserializers.py
@@ -98,7 +98,7 @@ def test_nested_nullable() -> None:
         },
         "mode": "format",
         "disks": {"main": "/dev/sda"},
-        "system_config": {"language": "en_US.utf-8", "keymap": "en"},
+        "system_config": {"language": "en_US.UTF-8", "keymap": "en"},
         "dry_run": False,
         "write_efi_boot_entries": False,
         "debug": False,
@@ -113,7 +113,7 @@ def test_nested_nullable() -> None:
         mode="format",
         disks={"main": "/dev/sda"},
         system_config=SystemConfig(
-            language="en_US.utf-8", keymap="en", ssh_keys_path=None
+            language="en_US.UTF-8", keymap="en", ssh_keys_path=None
         ),
         dry_run=False,
         write_efi_boot_entries=False,