diff -up kdelibs-3.5.10/configure.in.than kdelibs-3.5.10/configure.in
--- kdelibs-3.5.10/configure.in.than	2017-06-20 18:02:22.845910412 +0200
+++ kdelibs-3.5.10/configure.in	2017-06-20 18:03:09.058172814 +0200
@@ -692,10 +692,10 @@ AC_ARG_WITH(libidn,
   [], with_libidn=check)
 LIB_IDN=
 if test "x$with_libidn" != xno; then
-  AC_CHECK_HEADERS([idna.h punycode.h stringprep.h])
-  KDE_CHECK_LIB(idn, idna_to_ascii_4i, [
+  AC_CHECK_HEADERS([idn2.h])
+  KDE_CHECK_LIB(idn2, idn2_to_ascii_4i, [
     AC_DEFINE_UNQUOTED(HAVE_LIBIDN, 1, [Defined if you have libidn in your system])
-    LIB_IDN=-lidn
+    LIB_IDN=-lidn2
   ])
   if test "x$with_libidn" != xcheck && test -z "$LIB_IDN"; then
     AC_MSG_ERROR([--with-libidn was given, but test for libidn failed])
diff -up kdelibs-3.5.10/kdecore/configure.in.in.than kdelibs-3.5.10/kdecore/configure.in.in
--- kdelibs-3.5.10/kdecore/configure.in.in.than	2017-06-20 17:53:41.544511539 +0200
+++ kdelibs-3.5.10/kdecore/configure.in.in	2017-06-20 18:01:27.557989259 +0200
@@ -48,10 +48,10 @@ AC_ARG_WITH(libidn,
   [], with_libidn=check)
 LIB_IDN=
 if test "x$with_libidn" != xno; then
-  AC_CHECK_HEADERS([idna.h punycode.h stringprep.h])
-  KDE_CHECK_LIB(idn, idna_to_ascii_4i, [
+  AC_CHECK_HEADERS([idn2.h])
+  KDE_CHECK_LIB(idn2, idn2_to_ascii_4i, [
     AC_DEFINE_UNQUOTED(HAVE_LIBIDN, 1, [Defined if you have libidn in your system])
-    LIB_IDN=-lidn
+    LIB_IDN=-lidn2
   ])
   if test "x$with_libidn" != xcheck && test -z "$LIB_IDN"; then
     AC_MSG_ERROR([--with-libidn was given, but test for libidn failed])
diff -up kdelibs-3.5.10/kdecore/network/kresolver.cpp.than kdelibs-3.5.10/kdecore/network/kresolver.cpp
--- kdelibs-3.5.10/kdecore/network/kresolver.cpp.than	2017-06-21 12:55:55.733217103 +0200
+++ kdelibs-3.5.10/kdecore/network/kresolver.cpp	2017-06-21 13:27:38.956737181 +0200
@@ -49,8 +49,8 @@
 #include <qguardedptr.h>
 
 // IDN
-#ifdef HAVE_IDNA_H
-# include <idna.h>
+#ifdef HAVE_IDN2_H
+# include <idn2.h>
 #endif
 
 // KDE
@@ -1083,7 +1083,7 @@ static QStringList splitLabels(const QSt
 
 static QCString ToASCII(const QString& label)
 {
-#ifdef HAVE_IDNA_H
+#ifdef HAVE_IDN2_H
   // We have idna.h, so we can use the idna_to_ascii
   // function :)
 
@@ -1104,7 +1104,7 @@ static QCString ToASCII(const QString& l
     ucs4[i] = (unsigned long)label[i].unicode();
   ucs4[i] = 0;			// terminate with NUL, just to be on the safe side
 
-  if (idna_to_ascii_4i(ucs4, label.length(), buf, 0) == IDNA_SUCCESS)
+  if (idn2_to_ascii_4i(ucs4, label.length(), buf, 0|IDN2_NFC_INPUT|IDN2_NONTRANSITIONAL) == IDN2_OK)
     // success!
     retval = buf;
 
@@ -1117,7 +1117,7 @@ static QCString ToASCII(const QString& l
 
 static QString ToUnicode(const QString& label)
 {
-#ifdef HAVE_IDNA_H
+#ifdef HAVE_IDN2_H
   // We have idna.h, so we can use the idna_to_unicode
   // function :)
 
@@ -1131,7 +1131,7 @@ static QString ToUnicode(const QString&
   // try the same length for output
   ucs4_output = new Q_UINT32[outlen = label.length()];
 
-  idna_to_unicode_44i(ucs4_input, label.length(),
+  idn2_to_unicode_44i(ucs4_input, label.length(),
 		      ucs4_output, &outlen,
 		      0);
 
@@ -1141,7 +1141,7 @@ static QString ToUnicode(const QString&
       delete [] ucs4_output;
       ucs4_output = new Q_UINT32[outlen];
 
-      idna_to_unicode_44i(ucs4_input, label.length(),
+      idn2_to_unicode_44i(ucs4_input, label.length(),
 			  ucs4_output, &outlen,
 			  0);
     }