diff --git a/changes/autoconf-2.70 b/changes/autoconf-2.70
new file mode 100644
index 0000000000..27a9f243b1
--- /dev/null
+++ b/changes/autoconf-2.70
@@ -0,0 +1,3 @@
+  o Minor features (compilation):
+    - Make the autoconf script build correctly with autoconf versions 2.70
+      and later. Closes part of ticket 40335.
diff --git a/configure.ac b/configure.ac
index b821533654..16fdb626ee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -454,7 +454,11 @@ AM_CONDITIONAL(BUILD_MANPAGE, [test "x$enable_manpage" != "xno"])
 AM_CONDITIONAL(BUILD_HTML_DOCS, [test "x$enable_html_manual" != "xno"])
 
 AM_PROG_CC_C_O
-AC_PROG_CC_C99
+
+dnl Before autoconf 2.70, AC_PROG_CC_C99 is supposedly necessary for some
+dnl compilers if you wan't C99 support. Starting with 2.70, it is obsolete and
+dnl forbidden.
+m4_version_prereq([2.70], [:], [AC_PROG_CC_C99])
 
 AC_CACHE_CHECK([for Python 3], [tor_cv_PYTHON],
    [AC_PATH_PROGS_FEATURE_CHECK([PYTHON], [ \