diff --git a/ares/m4/cares-functions.m4 b/ares/m4/cares-functions.m4
index 695925a7c680da4a772831da7c9d2881ab7fe742..0169cf77ec03126ceeb3a86d89b8f9e7d83810cd 100644
--- a/ares/m4/cares-functions.m4
+++ b/ares/m4/cares-functions.m4
@@ -16,7 +16,7 @@
 #***************************************************************************
 
 # File version for 'aclocal' use. Keep it a single number.
-# serial 32
+# serial 33
 
 
 dnl CARES_INCLUDES_ARPA_INET
@@ -873,7 +873,10 @@ dnl Verify if getaddrinfo is available, prototyped, can
 dnl be compiled and seems to work. If all of these are
 dnl true, and usage has not been previously disallowed
 dnl with shell variable cares_disallow_getaddrinfo, then
-dnl HAVE_GETADDRINFO will be defined.
+dnl HAVE_GETADDRINFO will be defined. Additionally when
+dnl HAVE_GETADDRINFO gets defined this will also attempt
+dnl to find out if getaddrinfo happens to be threadsafe,
+dnl defining HAVE_GETADDRINFO_THREADSAFE when true.
 
 AC_DEFUN([CARES_CHECK_FUNC_GETADDRINFO], [
   AC_REQUIRE([CARES_INCLUDES_WS2TCPIP])dnl
@@ -887,6 +890,7 @@ AC_DEFUN([CARES_CHECK_FUNC_GETADDRINFO], [
   tst_compi_getaddrinfo="unknown"
   tst_works_getaddrinfo="unknown"
   tst_allow_getaddrinfo="unknown"
+  tst_tsafe_getaddrinfo="unknown"
   #
   AC_MSG_CHECKING([if getaddrinfo can be linked])
   AC_LINK_IFELSE([
@@ -1001,6 +1005,45 @@ AC_DEFUN([CARES_CHECK_FUNC_GETADDRINFO], [
   else
     AC_MSG_RESULT([no])
     ac_cv_func_getaddrinfo="no"
+    ac_cv_func_getaddrinfo_threadsafe="no"
+  fi
+  #
+  if test "$ac_cv_func_getaddrinfo" = "yes"; then
+    AC_MSG_CHECKING([if getaddrinfo is threadsafe])
+    case $host_os in
+      darwin[[12354678]].*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      darwin*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      dragonflybsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      freebsd[[1234]].* | freebsd5.[[1234]]*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      freebsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      linux*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      netbsd[[123]].*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      netbsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+    esac
+    AC_MSG_RESULT([$tst_tsafe_getaddrinfo])
+    if test "$tst_tsafe_getaddrinfo" = "yes"; then
+      AC_DEFINE_UNQUOTED(HAVE_GETADDRINFO_THREADSAFE, 1,
+        [Define to 1 if the getaddrinfo function is threadsafe.])
+      ac_cv_func_getaddrinfo_threadsafe="yes"
+    else
+      ac_cv_func_getaddrinfo_threadsafe="no"
+    fi
   fi
 ])
 
diff --git a/m4/curl-functions.m4 b/m4/curl-functions.m4
index c366779370b6220edb01394a087f167b7d5c7ae4..8cd99b07bb00c05113a8c59799fa44c80799c676 100644
--- a/m4/curl-functions.m4
+++ b/m4/curl-functions.m4
@@ -22,7 +22,7 @@
 #***************************************************************************
 
 # File version for 'aclocal' use. Keep it a single number.
-# serial 54
+# serial 55
 
 
 dnl CURL_INCLUDES_ARPA_INET
@@ -1497,7 +1497,10 @@ dnl Verify if getaddrinfo is available, prototyped, can
 dnl be compiled and seems to work. If all of these are
 dnl true, and usage has not been previously disallowed
 dnl with shell variable curl_disallow_getaddrinfo, then
-dnl HAVE_GETADDRINFO will be defined.
+dnl HAVE_GETADDRINFO will be defined. Additionally when
+dnl HAVE_GETADDRINFO gets defined this will also attempt
+dnl to find out if getaddrinfo happens to be threadsafe,
+dnl defining HAVE_GETADDRINFO_THREADSAFE when true.
 
 AC_DEFUN([CURL_CHECK_FUNC_GETADDRINFO], [
   AC_REQUIRE([CURL_INCLUDES_WS2TCPIP])dnl
@@ -1511,6 +1514,7 @@ AC_DEFUN([CURL_CHECK_FUNC_GETADDRINFO], [
   tst_compi_getaddrinfo="unknown"
   tst_works_getaddrinfo="unknown"
   tst_allow_getaddrinfo="unknown"
+  tst_tsafe_getaddrinfo="unknown"
   #
   AC_MSG_CHECKING([if getaddrinfo can be linked])
   AC_LINK_IFELSE([
@@ -1625,6 +1629,45 @@ AC_DEFUN([CURL_CHECK_FUNC_GETADDRINFO], [
   else
     AC_MSG_RESULT([no])
     ac_cv_func_getaddrinfo="no"
+    ac_cv_func_getaddrinfo_threadsafe="no"
+  fi
+  #
+  if test "$ac_cv_func_getaddrinfo" = "yes"; then
+    AC_MSG_CHECKING([if getaddrinfo is threadsafe])
+    case $host_os in
+      darwin[[12354678]].*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      darwin*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      dragonflybsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      freebsd[[1234]].* | freebsd5.[[1234]]*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      freebsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      linux*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+      netbsd[[123]].*)
+        tst_tsafe_getaddrinfo="no"
+        ;;
+      netbsd*)
+        tst_tsafe_getaddrinfo="yes"
+        ;;
+    esac
+    AC_MSG_RESULT([$tst_tsafe_getaddrinfo])
+    if test "$tst_tsafe_getaddrinfo" = "yes"; then
+      AC_DEFINE_UNQUOTED(HAVE_GETADDRINFO_THREADSAFE, 1,
+        [Define to 1 if the getaddrinfo function is threadsafe.])
+      ac_cv_func_getaddrinfo_threadsafe="yes"
+    else
+      ac_cv_func_getaddrinfo_threadsafe="no"
+    fi
   fi
 ])