diff --git a/configure.ac b/configure.ac
index 3f13b3a6..09a25384 100644
--- a/configure.ac
+++ b/configure.ac
@@ -189,18 +189,18 @@ else
 d])
 fi
 
-ac_save_CXXFLAGS="$CXXFLAGS"
+save_CXXFLAGS="$CXXFLAGS"
 CXXFLAGS=
 
 AX_CXX_COMPILE_STDCXX_11([noext], [optional])
 
 CXX1XCXXFLAGS="$CXXFLAGS"
-CXXFLAGS="$ac_save_CXXFLAGS"
+CXXFLAGS="$save_CXXFLAGS"
 AC_SUBST([CXX1XCXXFLAGS])
 
 AC_LANG_PUSH(C++)
 
-ac_save_CXXFLAGS="$CXXFLAGS"
+save_CXXFLAGS="$CXXFLAGS"
 CXXFLAGS="$CXXFLAGS $CXX1XCXXFLAGS"
 
 # Check that std::future is available.
@@ -236,7 +236,7 @@ std::map<int, int>().emplace(1, 2);
     [have_std_map_emplace=no
      AC_MSG_RESULT([no])])
 
-CXXFLAGS=$ac_save_CXXFLAGS
+CXXFLAGS=$save_CXXFLAGS
 
 AC_LANG_POP()
 
@@ -268,9 +268,9 @@ if test "x${have_zlib}" = "xno"; then
 fi
 
 # dl: openssl requires libdl when it is statically linked.
-ac_save_LIBS=$LIBS
+save_LIBS=$LIBS
 AC_SEARCH_LIBS([dlopen], [dl], [APPLDFLAGS="-ldl $APPLDFLAGS"], [], [])
-LIBS=$ac_save_LIBS
+LIBS=$save_LIBS
 
 # cunit
 PKG_CHECK_MODULES([CUNIT], [cunit >= 2.1], [have_cunit=yes], [have_cunit=no])
@@ -303,7 +303,7 @@ AM_CONDITIONAL([HAVE_CUNIT], [ test "x${have_cunit}" = "xyes" ])
 
 # libev (for src)
 # libev does not have pkg-config file.  Check it in an old way.
-ac_save_LIBS=$LIBS
+save_LIBS=$LIBS
 # android requires -lm for floor
 AC_CHECK_LIB([ev], [ev_time], [have_libev=yes], [have_libev=no], [-lm])
 if test "x${have_libev}" = "xyes"; then
@@ -315,7 +315,7 @@ if test "x${have_libev}" = "xyes"; then
     AC_SUBST([LIBEV_CFLAGS])
   fi
 fi
-LIBS=$ac_save_LIBS
+LIBS=$save_LIBS
 
 # openssl (for src)
 PKG_CHECK_MODULES([OPENSSL], [openssl >= 1.0.1],
@@ -361,7 +361,7 @@ AM_CONDITIONAL([HAVE_LIBXML2], [ test "x${have_libxml2}" = "xyes" ])
 # jemalloc
 have_jemalloc=no
 if test "x${request_jemalloc}" != "xno"; then
-  ac_save_LIBS=$LIBS
+  save_LIBS=$LIBS
   AC_SEARCH_LIBS([malloc_stats_print], [jemalloc], [have_jemalloc=yes], [],
                  [$PTHREAD_LDFLAGS])
 
@@ -377,7 +377,7 @@ if test "x${request_jemalloc}" != "xno"; then
     fi
   fi
 
-  LIBS=$ac_save_LIBS
+  LIBS=$save_LIBS
 
   if test "x${have_jemalloc}" = "xyes" &&
      test "x${jemalloc_libs}" != "xnone required"; then
@@ -654,8 +654,8 @@ AM_CONDITIONAL([ENABLE_TINY_NGHTTPD],
                [ test "x${have_epoll}" = "xyes" &&
                  test "x${have_timerfd_create}" = "xyes"])
 
-ac_save_CFLAGS=$CFLAGS
-ac_save_CXXFLAGS=$CXXFLAGS
+save_CFLAGS=$CFLAGS
+save_CXXFLAGS=$CXXFLAGS
 
 CFLAGS=
 CXXFLAGS=
@@ -719,8 +719,8 @@ fi
 WARNCFLAGS=$CFLAGS
 WARNCXXFLAGS=$CXXFLAGS
 
-CFLAGS=$ac_save_CFLAGS
-CXXFLAGS=$ac_save_CXXFLAGS
+CFLAGS=$save_CFLAGS
+CXXFLAGS=$save_CXXFLAGS
 
 AC_SUBST([WARNCFLAGS])
 AC_SUBST([WARNCXXFLAGS])