diff --git a/configure.ac b/configure.ac
index 690b6ad0a26e..b0697e3208db 100644
--- a/configure.ac
+++ b/configure.ac
@@ -128,7 +128,9 @@ PKG_PROG_PKG_CONFIG
 AC_PROG_CC([cc gcc])
 PHP_DETECT_ICC
 PHP_DETECT_SUNCC
-AC_PROG_CC_C99
+
+dnl AC_PROG_CC_C99 is obsolete with autoconf >= 2.70 yet necessary for <= 2.69.
+m4_version_prereq([2.70],,[AC_PROG_CC_C99])
 AC_PROG_CPP
 AC_USE_SYSTEM_EXTENSIONS
 AC_PROG_LN_S