diff --git a/webinstaller/app.py b/webinstaller/app.py
index f2d25a5..402bc08 100644
--- a/webinstaller/app.py
+++ b/webinstaller/app.py
@@ -125,7 +125,10 @@ def build_disk_config(boot_drive):
     device_mod = asyncio.run(
         suggest_single_disk_layout(
             device,
-            filesystem_type=FilesystemType.Ext4,
+            # archinstall renamed the enum members to ALL_CAPS at some point
+            # between when we wrote this and the pinned Arch live ISO version.
+            # The old name `Ext4` now raises AttributeError at install time.
+            filesystem_type=FilesystemType.EXT4,
             separate_home=False,
         )
     )