diff --git a/SimpleCom/SerialConnection.cpp b/SimpleCom/SerialConnection.cpp
index b8bf537..29f6e85 100644
--- a/SimpleCom/SerialConnection.cpp
+++ b/SimpleCom/SerialConnection.cpp
@@ -189,7 +189,7 @@ DWORD WINAPI StdOutRedirector(_In_ LPVOID lpParameter) {
 					return 0;
 				}
 				else {
-					MessageBox(param->parent_hwnd, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+					MessageBox(param->parent_hwnd, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 					return -1;
 				}
 			}
@@ -275,7 +275,7 @@ bool SimpleCom::SerialConnection::StdInRedirector(const HANDLE hSerial, const HA
 		SetEvent(hTermEvent);
 		// We can ignore ERROR_OPERATION_ABORTED because it would be intended.
 		if (e.GetErrorCode() != ERROR_OPERATION_ABORTED) {
-			MessageBox(_parent_hwnd, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+			MessageBox(_parent_hwnd, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 		}
 	}
 
diff --git a/SimpleCom/SerialDeviceScanner.cpp b/SimpleCom/SerialDeviceScanner.cpp
index 393a581..94f6ba6 100644
--- a/SimpleCom/SerialDeviceScanner.cpp
+++ b/SimpleCom/SerialDeviceScanner.cpp
@@ -74,7 +74,7 @@ static INT_PTR CALLBACK WaitDlgProc(HWND hDlg, UINT msg, WPARAM wParam, LPARAM l
 		}
 	}
 	catch (SimpleCom::WinAPIException& e) {
-		MessageBox(hDlg, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+		MessageBox(hDlg, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 		return FALSE;
 	}
 
diff --git a/SimpleCom/SerialSetup.cpp b/SimpleCom/SerialSetup.cpp
index 1860dd7..30fe62e 100644
--- a/SimpleCom/SerialSetup.cpp
+++ b/SimpleCom/SerialSetup.cpp
@@ -468,7 +468,7 @@ static INT_PTR CALLBACK SettingDlgProc(HWND hDlg, UINT msg, WPARAM wParam, LPARA
 		}
 	}
 	catch (SimpleCom::WinAPIException& e) {
-		MessageBox(hDlg, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+		MessageBox(hDlg, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 		return FALSE;
 	}
 
diff --git a/SimpleCom/SimpleCom.cpp b/SimpleCom/SimpleCom.cpp
index 9e70cc6..44f94b5 100644
--- a/SimpleCom/SimpleCom.cpp
+++ b/SimpleCom/SimpleCom.cpp
@@ -112,7 +112,7 @@ int _tmain(int argc, LPCTSTR argv[])
 		setup.SaveToDCB(&dcb);
 	}
 	catch (SimpleCom::WinAPIException& e) {
-		MessageBox(parent_hwnd, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+		MessageBox(parent_hwnd, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 		return -1;
 	}
 	catch (SimpleCom::SerialSetupException& e) {
@@ -157,7 +157,7 @@ int _tmain(int argc, LPCTSTR argv[])
 		}
 	}
 	catch (SimpleCom::WinAPIException& e) {
-		MessageBox(parent_hwnd, e.GetErrorText(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
+		MessageBox(parent_hwnd, e.GetErrorText().c_str(), e.GetErrorCaption(), MB_OK | MB_ICONERROR);
 		return -4;
 	}
 	catch (SimpleCom::SerialDeviceScanException& e) {
diff --git a/SimpleCom/WinAPIException.cpp b/SimpleCom/WinAPIException.cpp
index a96be09..4d65871 100644
--- a/SimpleCom/WinAPIException.cpp
+++ b/SimpleCom/WinAPIException.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2019, 2021, Yasumasa Suenaga
+ * Copyright (C) 2019, 2024, Yasumasa Suenaga
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -21,29 +21,24 @@
 #include "WinAPIException.h"
 #include "debug.h"
 
-static thread_local TCHAR fallback_error_text[100];
-
 
 SimpleCom::WinAPIException::WinAPIException(DWORD error_code, LPCTSTR error_caption) : _error_code(error_code),
-                                                                                       _error_caption(error_caption),
-	                                                                                   _error_text(nullptr)
+                                                                                       _error_caption(error_caption)
 {
-	DWORD result = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, _error_code, 0, reinterpret_cast<LPTSTR>(&_error_text), 0, NULL);
+	LPTSTR buf = nullptr;
+	TStringStream error_msg;
+	DWORD result = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, _error_code, 0, reinterpret_cast<LPTSTR>(&buf), 0, NULL);
 	if (result == 0) {
 		DWORD errcode = GetLastError();
-		_sntprintf_s(fallback_error_text, sizeof(fallback_error_text) / sizeof(TCHAR), _T("Error occured (%#x)"), _error_code);
-		_error_text = fallback_error_text;
+		error_msg << _T("Error occured (") << std::showbase << std::hex << _error_code << _T(")");
 
 		TStringStream msg;
 		msg << _T("Error occurred in FormatMessage (") << std::showbase << std::hex << errcode << _T(")");
 		debug::log(msg.str().c_str());
 	}
-}
-
-
-SimpleCom::WinAPIException::~WinAPIException()
-{
-	if ((_error_text != nullptr) && (_error_text != fallback_error_text) && (_error_code != -1)) {
-		LocalFree(_error_text);
+	else {
+		error_msg << buf << _T(" (") << std::showbase << std::hex << _error_code << _T(")");
+		LocalFree(buf);
 	}
-}
+	_error_text = error_msg.str();
+}
\ No newline at end of file
diff --git a/SimpleCom/WinAPIException.h b/SimpleCom/WinAPIException.h
index 5444a55..95f682b 100644
--- a/SimpleCom/WinAPIException.h
+++ b/SimpleCom/WinAPIException.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2019, 2021, Yasumasa Suenaga
+ * Copyright (C) 2019, 2024, Yasumasa Suenaga
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -32,13 +32,14 @@ namespace SimpleCom {
 	private:
 		DWORD _error_code;
 		LPCTSTR _error_caption;
-		LPTSTR _error_text;
+		TString _error_text;
 
 	public:
-		explicit WinAPIException(LPCTSTR error_caption, LPCTSTR error_text) : _error_code(-1), _error_caption(error_caption), _error_text(const_cast<LPTSTR>(error_text)) {}
+		explicit WinAPIException(LPCTSTR error_caption, LPCTSTR error_text) : _error_code(-1), _error_caption(error_caption), _error_text(error_text) {}
 		explicit WinAPIException(DWORD error_code) : WinAPIException(error_code, _T("SimpleCom")) {}
 		explicit WinAPIException(DWORD error_code, LPCTSTR error_caption);
-		virtual ~WinAPIException();
+		WinAPIException(const WinAPIException &ex) : _error_code(ex._error_code), _error_caption(ex._error_caption), _error_text(ex._error_text) {}
+		virtual ~WinAPIException() {};
 
 		WinAPIException& operator = (WinAPIException& rvalue) = delete;
 
@@ -50,7 +51,7 @@ namespace SimpleCom {
 			return _error_caption;
 		}
 
-		inline LPCTSTR GetErrorText() const noexcept {
+		inline TString GetErrorText() const noexcept {
 			return _error_text;
 		}
 	};
diff --git a/SimpleComTest/LogWriterTest.cpp b/SimpleComTest/LogWriterTest.cpp
index f0b6353..25bc267 100644
--- a/SimpleComTest/LogWriterTest.cpp
+++ b/SimpleComTest/LogWriterTest.cpp
@@ -37,7 +37,7 @@ namespace SimpleComTest
 			HANDLE hnd = CreateFile(TESTFILENAME, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
 			if (hnd == INVALID_HANDLE_VALUE) {
 				SimpleCom::WinAPIException ex(GetLastError());
-				Assert::Fail(ex.GetErrorText());
+				Assert::Fail(ex.GetErrorText().c_str());
 			}
 			DWORD fsize = GetFileSize(hnd, nullptr);
 			char* contents = new char[fsize + 1];
diff --git a/SimpleComTest/WinAPIExceptionTest.cpp b/SimpleComTest/WinAPIExceptionTest.cpp
index 20a851d..7de374f 100644
--- a/SimpleComTest/WinAPIExceptionTest.cpp
+++ b/SimpleComTest/WinAPIExceptionTest.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2023, Yasumasa Suenaga
+ * Copyright (C) 2023, 2024, Yasumasa Suenaga
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -49,7 +49,7 @@ namespace SimpleComTest
 		TEST_METHOD(MessageTest)
 		{
 			SimpleCom::WinAPIException e(TEST_ERRCODE);
-			Assert::AreEqual(expected, e.GetErrorText());
+			Assert::AreEqual(expected, e.GetErrorText().c_str());
 		}
 
 	};