diff --git a/reactos/dll/win32/aclui/sidcache.c b/reactos/dll/win32/aclui/sidcache.c
index 21b1a1abbfd..5e8db066912 100644
--- a/reactos/dll/win32/aclui/sidcache.c
+++ b/reactos/dll/win32/aclui/sidcache.c
@@ -158,7 +158,11 @@ ReferenceSidCacheMgr(IN HANDLE SidCacheMgr)
 static VOID
 DereferenceSidCacheMgr(IN PSIDCACHEMGR scm)
 {
-    InterlockedDecrement(&scm->RefCount);
+    if (InterlockedDecrement(&scm->RefCount) == 0)
+    {
+        /* Signal the lookup thread so it can terminate */
+        SetEvent(scm->LookupEvent);
+    }
 }