diff --git a/install.ps1 b/install.ps1
index 656ddcb3..a2992485 100644
--- a/install.ps1
+++ b/install.ps1
@@ -8,7 +8,7 @@ param(
 
 $ErrorActionPreference = "Stop"
 $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-$defaultInstallSha256 = "456d3e573f55c206ce3719160afee9b1d02fcfb7b6b53dceb33ebfd5c712a7fa"
+$defaultInstallSha256 = "6622a88280f46e21e7fac0adce72973211461cb6dc4af9cd3c5c1be8dd3aa842"
 $maximumInstallerBytes = 2MB
 $installerExit = 0
 $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
diff --git a/install.py b/install.py
index 685017ae..0ec3cfe1 100644
--- a/install.py
+++ b/install.py
@@ -1062,6 +1062,12 @@ def detect_platforms(os_type: str) -> list[tuple[str, Path]]:
                 found.append(("retroarch", ra_dir))
                 break
 
+        # The UWP/MSIX package (sideloaded, or Xbox in dev mode)
+        if not any(name == "retroarch" for name, _ in found):
+            uwp = _retroarch_uwp_system_dir()
+            if uwp is not None:
+                found.append(("retroarch", uwp))
+
         # Portable RetroArch referenced by LaunchBox
         lb_root = launchbox_root(os_type)
         if lb_root and not any(name == "retroarch" for name, _ in found):
@@ -1086,6 +1092,39 @@ def detect_platforms(os_type: str) -> list[tuple[str, Path]]:
     return found
 
 
+# Identity Name in pkg/msvc-uwp/RetroArch-msvcUWP/Package.appxmanifest.
+RETROARCH_UWP_ID = "1e4cf179-f3c2-404f-b9f3-cb2070a5aad8"
+
+
+def _retroarch_uwp_system_dir() -> Path | None:
+    """System directory of the RetroArch UWP package, if one is installed.
+
+    The package writes into its LocalState folder: uwp_main.cpp makes it the
+    home directory, configuration.c reads retroarch.cfg there, and
+    platform_uwp.c defaults the system directory to ~\\system. A `~` in the
+    config is therefore LocalState, not the user's profile.
+    """
+    local = os.environ.get("LOCALAPPDATA", "").strip()
+    if not local:
+        return None
+    states = sorted(Path(local, "Packages").glob(f"{RETROARCH_UWP_ID}_*/LocalState"))
+    if not states:
+        return None
+    state = states[0]
+    cfg = state / "retroarch.cfg"
+    try:
+        for line in cfg.read_text(encoding="utf-8", errors="replace").splitlines():
+            name, sep, value = line.strip().partition("=")
+            if sep and name.strip() == "system_directory":
+                value = value.strip().strip('"').strip("'")
+                if value.startswith("~"):
+                    return state / value[1:].lstrip("\\/")
+                break
+    except OSError:
+        return state / "system"
+    return _retroarch_cfg_dir(cfg, "system_directory", state, "system") or state / "system"
+
+
 def _bizhawk_unix_firmware() -> Path | None:
     """BizHawk's Firmware folder on Unix, where its data home says.
 
diff --git a/install.sh b/install.sh
index fc4de55b..c0488db0 100755
--- a/install.sh
+++ b/install.sh
@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="456d3e573f55c206ce3719160afee9b1d02fcfb7b6b53dceb33ebfd5c712a7fa"
+DEFAULT_INSTALL_SHA256="6622a88280f46e21e7fac0adce72973211461cb6dc4af9cd3c5c1be8dd3aa842"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {
diff --git a/tests/test_install.py b/tests/test_install.py
index 832222a9..88bef060 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -2405,5 +2405,33 @@ class BizHawkIsFoundWhereItReads(unittest.TestCase):
         self.assertIn('.get("emuhawk.exe")', source)
 
 
+
+class RetroArchUwpIsFound(unittest.TestCase):
+    """The UWP/MSIX RetroArch keeps retroarch.cfg and system/ in its
+    package's LocalState; no rule looked under %LOCALAPPDATA%\\Packages."""
+
+    def _state(self) -> Path:
+        local = Path(_tempdir(self))
+        state = local / "Packages" / f"{install.RETROARCH_UWP_ID}_abc123" / "LocalState"
+        state.mkdir(parents=True)
+        patcher = unittest.mock.patch.dict(os.environ, {"LOCALAPPDATA": str(local)})
+        patcher.start()
+        self.addCleanup(patcher.stop)
+        return state
+
+    def test_the_default_is_local_state_system(self):
+        state = self._state()
+        self.assertEqual(install._retroarch_uwp_system_dir(), state / "system")
+
+    def test_a_tilde_is_local_state(self):
+        state = self._state()
+        (state / "retroarch.cfg").write_text('system_directory = "~\\bios"\n')
+        self.assertEqual(install._retroarch_uwp_system_dir(), state / "bios")
+
+    def test_nothing_installed(self):
+        with unittest.mock.patch.dict(os.environ, {"LOCALAPPDATA": _tempdir(self)}):
+            self.assertIsNone(install._retroarch_uwp_system_dir())
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/wiki/installer.md b/wiki/installer.md
index 71aa1245..b409de27 100644
--- a/wiki/installer.md
+++ b/wiki/installer.md
@@ -299,6 +299,7 @@ found on one machine.
 | `retroarch.cfg` beside `retroarch.exe` (`C:\RetroArch-Win64`, `C:\RetroArch`, `Program Files\RetroArch`) | RetroArch (Windows) | `system_directory`; at default or without a config, `system` beside the exe |
 | `%APPDATA%\RetroArch\retroarch.cfg` | RetroArch (Windows) | `system_directory`, read when the exe folder has no config |
 | `%ProgramFiles(x86)%\Steam\steamapps\common\RetroArch\retroarch.cfg` | RetroArch (Steam) | `system_directory` |
+| `%LOCALAPPDATA%\Packages\1e4cf179-f3c2-404f-b9f3-cb2070a5aad8_*\LocalState` | RetroArch (UWP/MSIX package) | `system_directory` of the `retroarch.cfg` there, `~` meaning that folder; by default `LocalState\system` |
 | LaunchBox `Data\Emulators.xml` | RetroArch (portable) | the system directory that entry points at |
 | LaunchBox `Data\Emulators.xml` naming `EmuHawk.exe` | BizHawk (portable) | `Firmware` beside `EmuHawk.exe` |
 | `$BIZHAWK_DATA_HOME`, or `$XDG_DATA_HOME/emuhawk-monort-<version>` (Nix package) | BizHawk (Unix) | `Firmware` under it |