diff --git a/docs/TROUBLESHOOTING.md b/docs/TROUBLESHOOTING.md
index 72e096b..e5d1ad3 100644
--- a/docs/TROUBLESHOOTING.md
+++ b/docs/TROUBLESHOOTING.md
@@ -732,3 +732,36 @@ install the QuartzCore and OpenGL changes. Until updated, disable in-game
 VSync to use the game's frame cap, as the issue reporter confirmed. Physical
 scanout timing still depends on the driver and desktop compositor; the fix
 has standalone regression coverage but needs an in-game timing retest.
+
+## Installer aborts on `/proc/<pid>/fdinfo`
+
+[Issue #38](https://github.com/lucannez64/darling-lol/issues/38) reports an
+uncaught `ghc::filesystem::filesystem_error` with `Permission denied` on
+`/proc/<pid>/fdinfo`. `ghc::filesystem` is a C++ filesystem library, not evidence
+that the Riot installer is written in Haskell.
+
+An independent guest/native Vulkan probe reproduced this exact exception with
+MangoHud 0.8.4 enabled on 2026-10-18. MangoHud's `GPU_fdinfo::find_fd()` builds
+`/proc/<getpid()>/fdinfo` and uses a throwing directory iterator. Inside Darling,
+the native library's PID is in the guest PID namespace while its native `/proc`
+view can still refer to host processes: the probe's native PID 35 resolved to an
+inaccessible host process. The same probe completed Vulkan instance, device and
+swapchain creation with MangoHud disabled. This does not establish the cause of
+every installer abort; confirmation from the original reporter remains pending.
+
+The normal launcher now unsets `MANGOHUD` and exports `DISABLE_MANGOHUD=1` before
+runtime helpers start, including first-time installation. This disables inherited
+implicit MangoHud activation for the launched session without changing the host
+configuration. Do not wrap the launcher in `mangohud` or explicitly force its
+Vulkan layer. Updating these launcher scripts needs no Darling rebuild. For an
+older checkout, use:
+
+```sh
+env -u MANGOHUD DISABLE_MANGOHUD=1 ./scripts/installer.sh euw
+```
+
+Do not run the installer as root or change `/proc` permissions. If it still
+fails, include the exception and whether a host overlay was enabled; redact
+account tokens from logs.
+
+Upstream source: [MangoHud 0.8.4 fdinfo scan](https://github.com/flightlessmango/MangoHud/blob/v0.8.4/src/gpu_fdinfo.cpp#L9).
diff --git a/tools/riot-launcher-offline-check.py b/tools/riot-launcher-offline-check.py
index 0280d4e..58f1052 100644
--- a/tools/riot-launcher-offline-check.py
+++ b/tools/riot-launcher-offline-check.py
@@ -38,6 +38,7 @@ if record["command"] == "darling":
     record["flags"] = {{key: os.environ.get(key) for key in
         ("RCLOL_APP_ARG3", "RCLOL_APP_ARG3_SLOT", "RCLOL_UX_ARG2", "RCLOL_UX_ARG2_SLOT", "RCLOL_UX_ARG1", "RCLOL_APP_ARGS", "RCLOL_APP_ARG2", "DYLD_INSERT_LIBRARIES", "DYLD_LIBRARY_PATH", "DYLD_FRAMEWORK_PATH", "DARLING_XSHM_LIBRARY",
          "WAYLAND_DISPLAY", "XAUTHORITY", "DRI_PRIME", "MESA_NO_ERROR", "__GL_THREADED_OPTIMIZATIONS", "SHELL")}}
+record["hud"] = {{key: os.environ.get(key) for key in ("MANGOHUD", "DISABLE_MANGOHUD")}}
 with open({str(log)!r}, "a") as output:
     output.write(json.dumps(record) + "\\n")
 '''
@@ -59,6 +60,8 @@ with open({str(log)!r}, "a") as output:
         env["DYLD_INSERT_LIBRARIES"] = "/Users/offline-check/zzlogdir.dylib:/tmp/inherited.dylib"
         env["RCLOL_APP_ARGS"] = "--inherited-shim-argument"
         env["RCLOL_APP_ARG2"] = "--inherited-shim-argument-2"
+        env["MANGOHUD"] = "1"
+        env.pop("DISABLE_MANGOHUD", None)
         env["RCLOL_NATIVE_VPX"] = "1"
         env["RCLOL_LEAGUE_UX_TUNING"] = "1"
         # Inherited legacy settings must not re-enable inspection or unlimited frames.
@@ -90,6 +93,8 @@ with open({str(log)!r}, "a") as output:
         ], "unexpected automatic helper"
         launches = [r for r in records if r["command"] == "darling"]
         assert len(launches) == 1, "unexpected launch count"
+        for record in records:
+            assert record["hud"] == {"MANGOHUD": None, "DISABLE_MANGOHUD": "1"}, "MangoHud survived before a runtime helper"
         launch = launches[0]
         assert launch["fds"] == [0, 1, 2], f"inherited descriptors reached the guest: {launch['fds']}"
         assert all(launch["flags"][key] is None for key in (
@@ -106,17 +111,20 @@ with open({str(log)!r}, "a") as output:
         assert "--log-dir=/Users/offline-check/Library/Logs/Riot Games/Riot Client" in launch["args"], "absolute log directory lost"
         # An inherited injection must also be absent for first-time installation.
         env["RIOT_LAUNCHER_HOST"] = str(folder / "Install Riot.app/Contents/MacOS/RiotClientServices")
+        env["DISABLE_MANGOHUD"] = "0"  # Inherited settings cannot override launcher policy.
         subprocess.run(["sh", str(launcher)], env=env, check=True, capture_output=True, text=True)
         install = json.loads(log.read_text().splitlines()[-1])
         assert install["args"][0] == env["RIOT_LAUNCHER_HOST"]
         assert "--skip-to-install" in install["args"]
         assert not any(arg.startswith("--app-root=") for arg in install["args"])
         assert install["flags"]["DYLD_INSERT_LIBRARIES"] is None
+        assert install["hud"] == {"MANGOHUD": None, "DISABLE_MANGOHUD": "1"}
         env.pop("RIOT_LAUNCHER_HOST")
         env.pop("DYLD_INSERT_LIBRARIES")
         subprocess.run(["sh", str(launcher)], env=env, check=True, capture_output=True, text=True)
         clean = json.loads(log.read_text().splitlines()[-1])
         assert clean["flags"]["DYLD_INSERT_LIBRARIES"] is None
+        assert clean["hud"] == {"MANGOHUD": None, "DISABLE_MANGOHUD": "1"}
         # The opt-in host environment filter drops session metadata but never the launcher's GPU tuning.
         env.update({"RCLOL_FILTER_HOST_ENV": "1", "WAYLAND_DISPLAY": "wayland-0", "XAUTHORITY": "/tmp/xauth",
                     "DRI_PRIME": "1", "SHELL": "/bin/fish"})
@@ -127,7 +135,7 @@ with open({str(log)!r}, "a") as output:
         assert filtered["WAYLAND_DISPLAY"] is None and filtered["SHELL"] == "/bin/zsh", "host session metadata survived"
         assert (filtered["XAUTHORITY"], filtered["DRI_PRIME"]) == ("/tmp/xauth", "1"), "X11/GPU selection lost"
         assert (filtered["MESA_NO_ERROR"], filtered["__GL_THREADED_OPTIMIZATIONS"]) == ("1", "0"), "launcher GPU tuning lost"
-        print("LAUNCHER_OFFLINE pass=1 installed=PASS installer=PASS inherited_injection=absent runtime=preserved inherited_fds=closed host_env_filter=PASS")
+        print("LAUNCHER_OFFLINE pass=1 installed=PASS installer=PASS inherited_injection=absent runtime=preserved inherited_fds=closed host_env_filter=PASS mangohud=disabled")
 
 
 if __name__ == "__main__":
diff --git a/tools/run-riot-client.sh b/tools/run-riot-client.sh
index ed6fefd..148efd4 100755
--- a/tools/run-riot-client.sh
+++ b/tools/run-riot-client.sh
@@ -2,6 +2,11 @@
 # Launch Riot Client using the Darling runtime, without library injection.
 # Darling supplies Xlib Display pointers to EGL, so select X11 explicitly.
 set -eu
+# Native MangoHud uses the guest PID against the host /proc view and can abort
+# in GPU_fdinfo::find_fd (issue #38). Disable inherited implicit activation
+# before any helper can start Darling, including first-time installation.
+unset MANGOHUD
+export DISABLE_MANGOHUD=1
 # Native guest crashes created large system core files and exhausted this disk.
 # Address-only diagnostics suffice; bound this runner and its new namespace.
 if [ "${RCLOL_CORE_DUMPS:-0}" != 1 ]; then