diff --git a/configure.ac b/configure.ac
index a3c39bd06ddf7b2bf54f20213b5494b04c7b63ff..ee2fb6e0b8fda47ce7017677b4b5471e51830aaf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -963,6 +963,9 @@ case "$LIBIDN" in
                     ])
        if test "x$nolibidn" != "xtrue"; then
          curl_idn_msg="enabled"
+         dnl different versions of libidn have different setups of these:
+         AC_CHECK_FUNCS( idn_free )
+         AC_CHECK_HEADERS( idn-free.h )
        fi
                     
        ;;