diff --git a/ChangeLog b/ChangeLog
index 28c6a19aa..2b198b4bb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2021-02-17  Werner Lemberg  <wl@gnu.org>
+
+	[unix] Updates for autoconf 2.71.
+
+	This fixes warnings reported by autoupdate.
+
+	* builds/unix/ax_pthread.m4: Replace `as_echo` with `AS_ECHO`.
+
+	* builds/unix/configure.raw: Remove obsolete `AC_HEADER_STDC`.
+	Don't escape back quotes in messages for `AC_MSG_WARN`.
+
 2021-02-16  Werner Lemberg  <wl@gnu.org>
 
 	* builds/toplevel.mk: Fix previous commit.
diff --git a/builds/unix/ax_pthread.m4 b/builds/unix/ax_pthread.m4
index 1598d077f..507f182a8 100644
--- a/builds/unix/ax_pthread.m4
+++ b/builds/unix/ax_pthread.m4
@@ -386,7 +386,7 @@ if test "x$ax_pthread_clang" = "xyes"; then
              # step
              ax_pthread_save_ac_link="$ac_link"
              ax_pthread_sed='s/conftest\.\$ac_ext/conftest.$ac_objext/g'
-             ax_pthread_link_step=`$as_echo "$ac_link" | sed "$ax_pthread_sed"`
+             ax_pthread_link_step=`AS_ECHO(["$ac_link"]) | sed "$ax_pthread_sed"`
              ax_pthread_2step_ac_link="($ac_compile) && (echo ==== >&5) && ($ax_pthread_link_step)"
              ax_pthread_save_CFLAGS="$CFLAGS"
              for ax_pthread_try in '' -Qunused-arguments -Wno-unused-command-line-argument unknown; do
diff --git a/builds/unix/configure.raw b/builds/unix/configure.raw
index c0c8592de..09b5584f2 100644
--- a/builds/unix/configure.raw
+++ b/builds/unix/configure.raw
@@ -97,7 +97,6 @@ esac
 
 # checks for header files
 
-AC_HEADER_STDC
 AC_CHECK_HEADERS([fcntl.h unistd.h])
 
 
@@ -1022,7 +1021,7 @@ if test "x$PYTHON" != "xmissing"; then
 
   if test "x$have_py3" = "xyes"; then
     PIP="$PYTHON -m $PIP"
-    AC_MSG_CHECKING([for \`docwriter' Python module])
+    AC_MSG_CHECKING([for `docwriter' Python module])
     $PYTHON -m docwriter -h > /dev/null 2>&1
     if test "x$?" = "x0"; then
       have_docwriter=yes
@@ -1186,10 +1185,10 @@ Library configuration:
 
 if test $have_docwriter = no; then
   AC_MSG_WARN([
-  \`make refdoc' will fail since pip package \`docwriter' is not installed.
-  To install, run \`$PIP install docwriter', or to use a Python
-  virtual environment, run \`make refdoc-venv' (requires pip package
-  \`virtualenv'). These operations require Python >= 3.5.
+  `make refdoc' will fail since pip package `docwriter' is not installed.
+  To install, run `$PIP install docwriter', or to use a Python
+  virtual environment, run `make refdoc-venv' (requires pip package
+  `virtualenv').  These operations require Python >= 3.5.
   ])
 fi
 
@@ -1197,7 +1196,7 @@ fi
 
 if test $have_pthread = no; then
   AC_MSG_WARN([
-  \`FT_DEBUG_LOGGING' will not work since the \`pthread' library is not
+  `FT_DEBUG_LOGGING' will not work since the `pthread' library is not
   available.  This warning can be safely ignored if you don't plan to use
   this configuration macro.
   ])