diff --git a/mailnews/mime/src/nsMimeConverter.cpp b/mailnews/mime/src/nsMimeConverter.cpp
index d5210537e2d5..54117d58a7d8 100644
--- a/mailnews/mime/src/nsMimeConverter.cpp
+++ b/mailnews/mime/src/nsMimeConverter.cpp
@@ -107,7 +107,7 @@ nsMimeConverter::EncodeMimePartIIStr(const char    *header,
   char *utf8String;
 
   // Encoder needs utf-8 string.
-  if (MIME_ConvertString(mailCharset, "utf-8", header, &utf8String) != 0)
+  if (MIME_ConvertString(mailCharset, "UTF-8", header, &utf8String) != 0)
     return NS_ERROR_FAILURE;
 
   return EncodeMimePartIIStr_UTF8((const char *) utf8String, mailCharset, encodedWordSize, encodedString);
diff --git a/mailnews/mime/src/nsMsgHeaderParser.cpp b/mailnews/mime/src/nsMsgHeaderParser.cpp
index 2c2bb65beb51..b494d6d234f4 100644
--- a/mailnews/mime/src/nsMsgHeaderParser.cpp
+++ b/mailnews/mime/src/nsMsgHeaderParser.cpp
@@ -91,7 +91,7 @@ MimeCharsetConverterClass *nsMsgHeaderParser::GetUSAsciiToUtf8CharsetConverter()
 		m_USAsciiToUtf8CharsetConverter = new MimeCharsetConverterClass;
 		if (m_USAsciiToUtf8CharsetConverter)
 		{
-			nsresult rv = m_USAsciiToUtf8CharsetConverter->Initialize("us-ascii","utf-8", PR_FALSE);
+			nsresult rv = m_USAsciiToUtf8CharsetConverter->Initialize("us-ascii","UTF-8", PR_FALSE);
 			if (!NS_SUCCEEDED(rv))
 			{
 				delete m_USAsciiToUtf8CharsetConverter;