diff --git a/include/WinStd/COM.h b/include/WinStd/COM.h
index 1f11e79c..3eaceb59 100644
--- a/include/WinStd/COM.h
+++ b/include/WinStd/COM.h
@@ -27,13 +27,21 @@ namespace winstd
     class com_runtime_error : public num_runtime_error<HRESULT>
     {
     public:
+        ///
+        /// Constructs an exception
+        ///
+        /// \param[in] num Windows error code
+        ///
+        com_runtime_error(_In_ error_type num) : num_runtime_error<HRESULT>(num, message(num))
+        {}
+
         ///
         /// Constructs an exception
         ///
         /// \param[in] num  COM error code
         /// \param[in] msg  Error message
         ///
-        com_runtime_error(_In_ error_type num, _In_ const std::string& msg) : num_runtime_error<HRESULT>(num, msg)
+        com_runtime_error(_In_ error_type num, _In_ const std::string& msg) : num_runtime_error<HRESULT>(num, msg + ": " + message(num))
         {
         }
 
@@ -43,9 +51,29 @@ namespace winstd
         /// \param[in] num  COM error code
         /// \param[in] msg  Error message
         ///
-        com_runtime_error(_In_ error_type num, _In_opt_z_ const char* msg = nullptr) : num_runtime_error<HRESULT>(num, msg)
+        com_runtime_error(_In_ error_type num, _In_opt_z_ const char* msg) : num_runtime_error<HRESULT>(num, std::string(msg) + ": " + message(num))
         {
         }
+
+    protected:
+        ///
+        /// Returns a user-readable Windows error message.
+        /// As std::exception messages may only be char*, we use UTF-8 by convention.
+        ///
+        /// \sa [FormatMessage function](https://docs.microsoft.com/en-us/windows/desktop/api/winbase/nf-winbase-formatmessage)
+        ///
+        static std::string message(_In_ error_type num, _In_opt_ DWORD dwLanguageId = 0)
+        {
+            std::wstring wstr;
+            if (FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, 0, num, dwLanguageId, wstr, NULL)) {
+                // Stock Windows error messages contain CRLF. Well... Trim all the trailing white space.
+                wstr.erase(wstr.find_last_not_of(L" \t\n\r\f\v") + 1);
+            } else
+                sprintf(wstr, num >= 0x10000 ? L"Error 0x%X" : L"Error %u", num);
+            std::string str;
+            WideCharToMultiByte(CP_UTF8, 0, wstr, str, NULL, NULL);
+            return str;
+        }
     };
 
     /// @}