diff --git a/packages/cultnet-ts/src/idunn-runtime-authority.ts b/packages/cultnet-ts/src/idunn-runtime-authority.ts
index de4f3579..ea07ba27 100644
--- a/packages/cultnet-ts/src/idunn-runtime-authority.ts
+++ b/packages/cultnet-ts/src/idunn-runtime-authority.ts
@@ -605,8 +605,7 @@ export function systemdListenPidMatches(listenPid: string | undefined, processPi
 }
 
 function readDescriptor(descriptor: number): Buffer {
-  const fdPath = `/proc/self/fd/${descriptor}`;
-  return fs.readFileSync(fdPath);
+  return fs.readFileSync(descriptor);
 }
 
 function privateKeyFromSeed(seed: Uint8Array): crypto.KeyObject {
diff --git a/packages/cultnet-ts/test/idunn-runtime-authority.test.ts b/packages/cultnet-ts/test/idunn-runtime-authority.test.ts
index cfd2b5a4..a2277c92 100644
--- a/packages/cultnet-ts/test/idunn-runtime-authority.test.ts
+++ b/packages/cultnet-ts/test/idunn-runtime-authority.test.ts
@@ -100,8 +100,8 @@ test("opens Idunn's machine-bound identity and signs the exact Expected incarnat
   process.env.LISTEN_FDNAMES = "gamecult-idunn-runtime-activation-key:gamecult-runtime-presence-identity";
   const realReadFileSync = fs.readFileSync.bind(fs);
   mock.method(fs, "readFileSync", (filePath: fs.PathOrFileDescriptor, ...args: unknown[]) => {
-    if (filePath === "/proc/self/fd/3") return activationSeed;
-    if (filePath === "/proc/self/fd/4") return providerCredential;
+    if (filePath === 3) return activationSeed;
+    if (filePath === 4) return providerCredential;
     if (filePath === "/etc/machine-id") return machineId;
     return realReadFileSync(filePath as never, ...args as never[]);
   });