diff --git a/src/api/sessions.controller.ts b/src/api/sessions.controller.ts
index dd166ef4..6dbb51e6 100644
--- a/src/api/sessions.controller.ts
+++ b/src/api/sessions.controller.ts
@@ -50,7 +50,7 @@ class SessionsController {
     this.lock = new AsyncLock({ maxPending: Infinity });
   }
 
-  private withLock(name, fn) {
+  private withLock(name: string, fn: () => any) {
     return this.lock.acquire(name, fn);
   }