diff --git a/install.ps1 b/install.ps1
index 58bbdef8..3f72df34 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 = "142edea98e646ed11e27052d3dd02125a27d4cdb7ee04392e6af8fcd28f9762f"
+$defaultInstallSha256 = "bf522ef64ecbefc14202a879b6c943e44939dfda37eb416b1897070ad7cefa85"
 $maximumInstallerBytes = 2MB
 $installerExit = 0
 $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }
diff --git a/install.py b/install.py
index 0d54fde9..2f923d4d 100644
--- a/install.py
+++ b/install.py
@@ -567,11 +567,19 @@ def _windows_retroarch_dirs() -> list[Path]:
 
 def _macos_retroarch_base() -> Path:
     """Where RetroArch on macOS keeps its system folder by default:
-    ~/Documents/RetroArch, or Application Support/RetroArch when that folder
-    holds portable.txt (platform_darwin.m)."""
+    ~/Documents/RetroArch, or Application Support/RetroArch for a portable
+    install. The Steam build is always portable (platform_darwin.m, `#if
+    HAVE_STEAM portable = YES`), with no portable.txt to say so: its
+    bundle under Steam's library, and no other RetroArch.app, mark it."""
     support = Path.home() / "Library" / "Application Support" / "RetroArch"
     if (support / "portable.txt").is_file():
         return support
+    steam = (
+        Path.home() / "Library" / "Application Support" / "Steam" / "steamapps"
+        / "common" / "RetroArch" / "RetroArch.app"
+    )
+    if steam.is_dir() and not Path("/Applications/RetroArch.app").is_dir():
+        return support
     return Path.home() / "Documents" / "RetroArch"
 
 
diff --git a/install.sh b/install.sh
index 2545286f..8958d351 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="142edea98e646ed11e27052d3dd02125a27d4cdb7ee04392e6af8fcd28f9762f"
+DEFAULT_INSTALL_SHA256="bf522ef64ecbefc14202a879b6c943e44939dfda37eb416b1897070ad7cefa85"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {
diff --git a/tests/test_install.py b/tests/test_install.py
index e11887ef..baac8bbb 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -2826,5 +2826,20 @@ class WindowsSeenFromWsl(unittest.TestCase):
             self.assertEqual(os.environ["ProgramFiles"], "")
 
 
+class SteamRetroArchOnMacIsPortable(unittest.TestCase):
+    """platform_darwin.m makes the Steam build portable (HAVE_STEAM) with no
+    portable.txt: a default system_directory is Application Support's, and
+    the installer took ~/Documents/RetroArch/system."""
+
+    def test_the_steam_bundle_moves_the_base(self):
+        home = Path(_tempdir(self))
+        support = home / "Library" / "Application Support"
+        with unittest.mock.patch.dict(os.environ, {"HOME": str(home)}), \
+                unittest.mock.patch.object(Path, "home", return_value=home):
+            self.assertEqual(install._macos_retroarch_base(), home / "Documents" / "RetroArch")
+            (support / "Steam/steamapps/common/RetroArch/RetroArch.app").mkdir(parents=True)
+            self.assertEqual(install._macos_retroarch_base(), support / "RetroArch")
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/wiki/installer.md b/wiki/installer.md
index e7e14283..faa6298b 100644
--- a/wiki/installer.md
+++ b/wiki/installer.md
@@ -306,7 +306,7 @@ WSL does not pass them. A forced `--platform retrobat` falls back to
 | `~/.var/app/org.libretro.RetroArch/config/retroarch/retroarch.cfg` | RetroArch (Flatpak) | `system_directory` |
 | `~/snap/retroarch/current/.config/retroarch/retroarch.cfg` | RetroArch (Snap) | `system_directory` |
 | `~/.config/retroarch/retroarch.cfg` | RetroArch (native) | `system_directory` |
-| `~/Library/Application Support/RetroArch/config/retroarch.cfg` | RetroArch (macOS) | `system_directory`; at default, `~/Documents/RetroArch/system` (portable: `Application Support/RetroArch/system`) |
+| `~/Library/Application Support/RetroArch/config/retroarch.cfg` | RetroArch (macOS) | `system_directory`; at default, `~/Documents/RetroArch/system` (portable, Steam build included: `Application Support/RetroArch/system`) |
 | `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` |