diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index 01d7f0eea9..35ce27fb31 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -3056,7 +3056,7 @@ GetSpinLockProperties (
 SPIN_LOCK *
 EFIAPI
 InitializeSpinLock (
-  IN      SPIN_LOCK                 *SpinLock
+  OUT      SPIN_LOCK                 *SpinLock
   );