--- a/src/nhttpd/yhttpd_core/yhook.cpp
+++ b/src/nhttpd/yhttpd_core/yhook.cpp
@@ -13,6 +13,46 @@
 // yhttpd
 #include "yhook.h"
 #include "helper.h"
+
+std::string iso_8859_1_to_utf8(std::string &str)
+{
+    std::string strOut;
+    for (std::string::iterator it = str.begin(); it != str.end(); ++it)
+    {
+        uint8_t ch = *it;
+        if (ch < 0x80) {
+            strOut.push_back(ch);
+        }
+        else {
+            strOut.push_back(0xc0 | ch >> 6);
+            strOut.push_back(0x80 | (ch & 0x3f));
+        }
+    }
+    return strOut;
+}
+
+bool utf8_check_is_valid(const std::string &str)
+{
+    int c,i,ix,n,j;
+    for (i=0, ix=str.length(); i < ix; i++)
+    {
+        c = (unsigned char) str[i];
+        //if (c==0x09 || c==0x0a || c==0x0d || (0x20 <= c && c <= 0x7e) ) n = 0; // is_printable_ascii
+        if (0x00 <= c && c <= 0x7f) n=0; // 0bbbbbbb
+        else if ((c & 0xE0) == 0xC0) n=1; // 110bbbbb
+        else if ( c==0xed && i<(ix-1) && ((unsigned char)str[i+1] & 0xa0)==0xa0) return false; //U+d800 to U+dfff
+        else if ((c & 0xF0) == 0xE0) n=2; // 1110bbbb
+        else if ((c & 0xF8) == 0xF0) n=3; // 11110bbb
+        //else if (($c & 0xFC) == 0xF8) n=4; // 111110bb //byte 5, unnecessary in 4 byte UTF-8
+        //else if (($c & 0xFE) == 0xFC) n=5; // 1111110b //byte 6, unnecessary in 4 byte UTF-8
+        else return false;
+        for (j=0; j<n && i<ix; j++) { // n bytes matching 10bbbbbb follow ?
+            if ((++i == ix) || (( (unsigned char)str[i] & 0xC0) != 0x80))
+                return false;
+        }
+    }
+    return true;
+}
 
 //=============================================================================
 // Constructor & Ceconstructor
@@ -542,7 +582,7 @@
 	std::string result = "";
 	switch (outType) {
 	case xml:
-		result = convert_UTF8_To_UTF8_XML(_content.c_str());
+		result = convert_UTF8_To_UTF8_XML(utf8_check_is_valid(_content) ? _content.c_str() : iso_8859_1_to_utf8(_content).c_str());
 		break;
 	case json:
 		result = json_convert_string(_content);