diff --git a/configure.ac b/configure.ac
index 012486666..6d0c7d096 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,7 +25,8 @@ AH_BOTTOM([
 
 AC_LANG([C])
 AC_PROG_CC
-AC_PROG_CC_C99
+# autoconf 2.70 obsoletes AC_PROG_CC_C99 and includes it in AC_PROG_CC
+m4_version_prereq([2.70],[],[AC_PROG_CC_C99])
 AM_PROG_CC_C_O
 AC_PROG_RANLIB
 PKG_PROG_PKG_CONFIG([0.23])