diff --git a/include/WinStd/Win.h b/include/WinStd/Win.h
index a779872e..ddf06ada 100644
--- a/include/WinStd/Win.h
+++ b/include/WinStd/Win.h
@@ -832,11 +832,11 @@ namespace winstd
         ///
         /// Construct the impersonator and impersonates the given user
         ///
-        /// \param[in] hToken  A handle to a primary or impersonation access token that represents a logged-on user
+        /// \param[in] hToken  A handle to a primary or impersonation access token that represents a logged-on user or NULL for no impersonation.
         ///
         /// \sa [ImpersonateLoggedOnUser function](https://msdn.microsoft.com/en-us/library/windows/desktop/aa378612.aspx)
         ///
-        user_impersonator(_In_ HANDLE hToken);
+        user_impersonator(_In_opt_ HANDLE hToken);
 
         ///
         /// Reverts to current user and destructs the impersonator
diff --git a/src/Win.cpp b/src/Win.cpp
index 2bcd3cb1..b60a9dc4 100644
--- a/src/Win.cpp
+++ b/src/Win.cpp
@@ -283,9 +283,9 @@ winstd::actctx_activator::~actctx_activator()
 // winstd::user_impersonator
 //////////////////////////////////////////////////////////////////////
 
-winstd::user_impersonator::user_impersonator(_In_ HANDLE hToken)
+winstd::user_impersonator::user_impersonator(_In_opt_ HANDLE hToken)
 {
-    m_cookie = ImpersonateLoggedOnUser(hToken);
+    m_cookie = hToken && ImpersonateLoggedOnUser(hToken);
 }