diff --git a/include/WinStd/COM.h b/include/WinStd/COM.h
index 4fd8d0f4..56d87c4c 100644
--- a/include/WinStd/COM.h
+++ b/include/WinStd/COM.h
@@ -968,9 +968,9 @@ namespace winstd
         ///
         /// \sa [VariantChangeType function](https://msdn.microsoft.com/en-us/library/windows/desktop/ms221258.aspx)
         ///
-        inline HRESULT change_type(_In_ VARTYPE vt, _In_opt_ USHORT wFlags = 0)
+        inline HRESULT change_type(_In_ VARTYPE _vt, _In_opt_ USHORT wFlags = 0)
         {
-            return VariantChangeType(this, this, wFlags, vt);
+            return VariantChangeType(this, this, wFlags, _vt);
         }
 
     private:
diff --git a/include/WinStd/Common.h b/include/WinStd/Common.h
index a5a03af7..b48116bb 100644
--- a/include/WinStd/Common.h
+++ b/include/WinStd/Common.h
@@ -1727,10 +1727,10 @@ inline int vsprintf(_Out_ std::basic_string<_Elem, _Traits, _Ax> &str, _In_z_ _P
     } else {
         for (size_t capacity = 2*WINSTD_STACK_BUFFER_BYTES/sizeof(_Elem);; capacity *= 2) {
             // Allocate on heap and retry.
-            std::unique_ptr<_Elem[]> buf(new _Elem[capacity]);
-            count = vsnprintf(buf.get(), capacity - 1, format, arg);
+            std::unique_ptr<_Elem[]> buf_dyn(new _Elem[capacity]);
+            count = vsnprintf(buf_dyn.get(), capacity - 1, format, arg);
             if (count >= 0) {
-                str.assign(buf.get(), count);
+                str.assign(buf_dyn.get(), count);
                 break;
             }
         }