diff --git a/Makefile.inc b/Makefile.inc
index c524802e..2a2c7842 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -3,14 +3,14 @@ ares_query.c ares__close_sockets.c ares_free_string.c ares_search.c	\
 ares__get_hostent.c ares_gethostbyaddr.c ares_send.c ares__read_line.c	\
 ares_gethostbyname.c ares_strerror.c ares_cancel.c ares_init.c		\
 ares_timeout.c ares_destroy.c ares_mkquery.c ares_version.c		\
-ares_expand_name.c ares_parse_a_reply.c windows_port.c			\
+ares_expand_name.c ares_parse_a_reply.c windows_port.c ares_strdup.c	\
 ares_expand_string.c ares_parse_ptr_reply.c ares_parse_aaaa_reply.c	\
 ares_getnameinfo.c inet_net_pton.c bitncmp.c inet_ntop.c		\
 ares_parse_ns_reply.c ares_llist.c ares__timeval.c
 
 HHEADERS = ares.h ares_private.h setup.h ares_dns.h ares_version.h          \
            nameser.h inet_net_pton.h inet_ntop.h ares_ipv6.h bitncmp.h      \
-           setup_once.h ares_llist.h
+           setup_once.h ares_llist.h ares_strdup.h
 
 MANPAGES= ares_destroy.3 ares_expand_name.3 ares_expand_string.3 ares_fds.3 \
  ares_free_hostent.3 ares_free_string.3 ares_gethostbyaddr.3		    \
diff --git a/ares_private.h b/ares_private.h
index 38269b02..877985bc 100644
--- a/ares_private.h
+++ b/ares_private.h
@@ -94,6 +94,11 @@
 #include "ares_ipv6.h"
 #include "ares_llist.h"
 
+#ifndef HAVE_STRDUP
+#  include "ares_strdup.h"
+#  define strdup(ptr) ares_strdup(ptr)
+#endif
+
 struct query;
 
 struct send_request {
diff --git a/ares_strdup.c b/ares_strdup.c
new file mode 100644
index 00000000..284a8136
--- /dev/null
+++ b/ares_strdup.c
@@ -0,0 +1,43 @@
+
+/* $Id$ */
+
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "setup.h"
+#include "ares_strdup.h"
+
+#ifndef HAVE_STRDUP
+char *ares_strdup(const char *s1)
+{
+  size_t sz;
+  char * s2;
+
+  if(s1) {
+    sz = strlen(s1);
+    if(sz < (size_t)-1) {
+      sz++;
+      if(sz < ((size_t)-1) / sizeof(char)) {
+        s2 = malloc(sz * sizeof(char));
+        if(s2) {
+          memcpy(s2, s1, sz * sizeof(char));
+          return s2;
+        }
+      }
+    }
+  }
+  return (char *)NULL;
+}
+#endif
diff --git a/ares_strdup.h b/ares_strdup.h
new file mode 100644
index 00000000..4a649cb2
--- /dev/null
+++ b/ares_strdup.h
@@ -0,0 +1,27 @@
+#ifndef HEADER_CARES_STRDUP_H
+#define HEADER_CARES_STRDUP_H
+
+/* $Id$ */
+
+/* Copyright 1998 by the Massachusetts Institute of Technology.
+ *
+ * Permission to use, copy, modify, and distribute this
+ * software and its documentation for any purpose and without
+ * fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright
+ * notice and this permission notice appear in supporting
+ * documentation, and that the name of M.I.T. not be used in
+ * advertising or publicity pertaining to distribution of the
+ * software without specific, written prior permission.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ */
+
+#include "setup.h"
+
+#ifndef HAVE_STRDUP
+extern char *ares_strdup(const char *s1);
+#endif
+
+#endif /* HEADER_CARES_STRDUP_H */
diff --git a/config-win32.h b/config-win32.h
index eb8fed72..5e26fa61 100644
--- a/config-win32.h
+++ b/config-win32.h
@@ -79,6 +79,9 @@
 /* Define if you have the ioctlsocket function.  */
 #define HAVE_IOCTLSOCKET 1
 
+/* Define if you have the strdup function. */
+#define HAVE_STRDUP 1
+
 /* Define if you have the recv function. */
 #define HAVE_RECV 1
 
diff --git a/configure.ac b/configure.ac
index 745a39cb..80b5be6f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -643,6 +643,8 @@ CURL_CHECK_FUNC_RECVFROM
 CURL_CHECK_FUNC_SEND
 CURL_CHECK_MSG_NOSIGNAL
 
+CARES_CHECK_FUNC_STRDUP
+
 dnl check for AF_INET6
 CARES_CHECK_CONSTANT(
   [
diff --git a/m4/cares-functions.m4 b/m4/cares-functions.m4
new file mode 100644
index 00000000..3d263caf
--- /dev/null
+++ b/m4/cares-functions.m4
@@ -0,0 +1,126 @@
+#***************************************************************************
+# $Id$
+#
+# Copyright (C) 2008 by Daniel Stenberg et al
+#
+# Permission to use, copy, modify, and distribute this software and its
+# documentation for any purpose and without fee is hereby granted, provided
+# that the above copyright notice appear in all copies and that both that
+# copyright notice and this permission notice appear in supporting
+# documentation, and that the name of M.I.T. not be used in advertising or
+# publicity pertaining to distribution of the software without specific,
+# written prior permission.  M.I.T. makes no representations about the
+# suitability of this software for any purpose.  It is provided "as is"
+# without express or implied warranty.
+#
+#***************************************************************************
+
+# File version for 'aclocal' use. Keep it a single number.
+# serial 1
+
+
+dnl CARES_INCLUDES_STRING
+dnl -------------------------------------------------
+dnl Set up variable with list of headers that must be
+dnl included when string.h is to be included.
+
+AC_DEFUN([CARES_INCLUDES_STRING], [
+cares_includes_string="\
+/* includes start */
+#ifdef HAVE_SYS_TYPES_H
+#  include <sys/types.h>
+#endif
+#ifdef HAVE_STRING_H
+#  include <string.h>
+#endif
+/* includes end */"
+  AC_CHECK_HEADERS(
+    sys/types.h string.h,
+    [], [], [$cares_includes_string])
+])
+
+
+dnl CARES_CHECK_FUNC_STRDUP
+dnl -------------------------------------------------
+dnl Verify if strdup is available, prototyped, and
+dnl can be compiled. If all of these are true, and
+dnl usage has not been previously disallowed with
+dnl shell variable cares_disallow_strdup, then
+dnl HAVE_STRDUP will be defined.
+
+AC_DEFUN([CARES_CHECK_FUNC_STRDUP], [
+  AC_REQUIRE([CARES_INCLUDES_STRING])dnl
+  #
+  tst_links_strdup="unknown"
+  tst_proto_strdup="unknown"
+  tst_compi_strdup="unknown"
+  tst_allow_strdup="unknown"
+  #
+  AC_MSG_CHECKING([if strdup can be linked])
+  AC_LINK_IFELSE([
+    AC_LANG_FUNC_LINK_TRY([strdup])
+  ],[
+    AC_MSG_RESULT([yes])
+    tst_links_strdup="yes"
+  ],[
+    AC_MSG_RESULT([no])
+    tst_links_strdup="no"
+  ])
+  #
+  if test "$tst_links_strdup" = "yes"; then
+    AC_MSG_CHECKING([if strdup is prototyped])
+    AC_EGREP_CPP([strdup],[
+      $cares_includes_string
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_proto_strdup="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_proto_strdup="no"
+    ])
+  fi
+  #
+  if test "$tst_proto_strdup" = "yes"; then
+    AC_MSG_CHECKING([if strdup is compilable])
+    AC_COMPILE_IFELSE([
+      AC_LANG_PROGRAM([[
+        $cares_includes_string
+      ]],[[
+        if(0 != strdup(0))
+          return 1;
+      ]])
+    ],[
+      AC_MSG_RESULT([yes])
+      tst_compi_strdup="yes"
+    ],[
+      AC_MSG_RESULT([no])
+      tst_compi_strdup="no"
+    ])
+  fi
+  #
+  if test "$tst_compi_strdup" = "yes"; then
+    AC_MSG_CHECKING([if strdup usage allowed])
+    if test "x$cares_disallow_strdup" != "xyes"; then
+      AC_MSG_RESULT([yes])
+      tst_allow_strdup="yes"
+    else
+      AC_MSG_RESULT([no])
+      tst_allow_strdup="no"
+    fi
+  fi
+  #
+  AC_MSG_CHECKING([if strdup might be used])
+  if test "$tst_links_strdup" = "yes" &&
+     test "$tst_proto_strdup" = "yes" &&
+     test "$tst_compi_strdup" = "yes" &&
+     test "$tst_allow_strdup" = "yes"; then
+    AC_MSG_RESULT([yes])
+    AC_DEFINE_UNQUOTED(HAVE_STRDUP, 1,
+      [Define to 1 if you have the strdup function.])
+    ac_cv_func_strdup="yes"
+  else
+    AC_MSG_RESULT([no])
+    ac_cv_func_strdup="no"
+  fi
+])
+
diff --git a/setup.h b/setup.h
index 9fe081bb..5ae3b9e4 100644
--- a/setup.h
+++ b/setup.h
@@ -150,11 +150,6 @@ int ares_strcasecmp(const char *s1, const char *s2);
    same */
 #define strncasecmp(a,b,c) ares_strncasecmp(a,b,c)
 #define strcasecmp(a,b) ares_strcasecmp(a,b)
-#ifdef _MSC_VER
-#  if _MSC_VER >= 1400
-#    define strdup(a) _strdup(a)
-#  endif
-#endif
 #endif
 
 /* IPv6 compatibility */