diff --git a/reactos/dll/ntdll/def/ntdll.pspec b/reactos/dll/ntdll/def/ntdll.pspec
index d9ca50edbcf..58b90e9765b 100644
--- a/reactos/dll/ntdll/def/ntdll.pspec
+++ b/reactos/dll/ntdll/def/ntdll.pspec
@@ -418,7 +418,7 @@
 @ stdcall RtlAcquireSRWLockExclusive(ptr)
 @ stdcall RtlAcquireSRWLockShared(ptr)
 @ stdcall RtlActivateActivationContext(long ptr ptr)
-//@ stdcall RtlActivateActivationContextEx
+@ stdcall RtlActivateActivationContextEx(long ptr ptr ptr)
 @ fastcall RtlActivateActivationContextUnsafeFast(ptr ptr)
 @ stdcall RtlAddAccessAllowedAce(ptr long long ptr)
 @ stdcall RtlAddAccessAllowedAceEx(ptr long long long ptr)