diff --git a/configure.ac b/configure.ac
index cecb324..5ec18c6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,7 +1,7 @@
 #                                               -*- Autoconf -*-
 # Process this file with autoconf to produce a configure script.
 
-AC_PREREQ([2.69])
+AC_PREREQ([2.68])
 AC_INIT(calcelestial, 0.1, post@steffenvogel.de)
 AC_CONFIG_SRCDIR([src/calcelestial.c])
 AC_CONFIG_HEADERS([config.h])