diff --git a/Src/Common/UnicodeString.cpp b/Src/Common/UnicodeString.cpp
index 9805d014888..7673fa85184 100644
--- a/Src/Common/UnicodeString.cpp
+++ b/Src/Common/UnicodeString.cpp
@@ -174,7 +174,7 @@ String format_arg_list(const TCHAR *fmt, va_list args)
 	std::vector<TCHAR> buffer(length, 0);
 	while (result == -1)
 	{
-		result = _vsntprintf_s(&buffer[0], length, length, fmt, args);
+		result = _vsntprintf_s(&buffer[0], length, _TRUNCATE, fmt, args);
 		length *= 2;
 		buffer.resize(length, 0);
 	}
diff --git a/Testing/GoogleTest/UnicodeString/UnicodeString_test.cpp b/Testing/GoogleTest/UnicodeString/UnicodeString_test.cpp
index 851f69a04cf..7c882699c2f 100644
--- a/Testing/GoogleTest/UnicodeString/UnicodeString_test.cpp
+++ b/Testing/GoogleTest/UnicodeString/UnicodeString_test.cpp
@@ -354,4 +354,11 @@ namespace
 		EXPECT_NE(0, strutils::compare_nocase(_T("abc"), _T("aDc")));
 	}
 
+	TEST_F(UnicodeStringTest, Format1)
+	{
+		EXPECT_TRUE(String(255, ' ') == strutils::format(_T("%s"), String(255, ' ').c_str()));
+		EXPECT_TRUE(String(256, ' ') == strutils::format(_T("%s"), String(256, ' ').c_str()));
+		EXPECT_TRUE(String(257, ' ') == strutils::format(_T("%s"), String(257, ' ').c_str()));
+	}
+
 }  // namespace