Copy va_lists by using va_copy, not by just assigning them.
diff --git a/configure.ac b/configure.ac
index 3e34fe9..37aeb2e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -447,6 +447,34 @@
AC_DEFINE(HAVE_PPDEV, 1, [Define if we can use ppdev.h for parallel port access])
fi
+dnl **** Check for va_copy ****
+AC_CACHE_CHECK([for va_copy], ac_cv_c_va_copy,
+ AC_TRY_LINK(
+ [#include <stdarg.h>],
+ [va_list ap1, ap2;
+ va_copy(ap1,ap2);
+ ],
+ [ac_cv_c_va_copy="yes"],
+ [ac_cv_c_va_copy="no"])
+ )
+if test "$ac_cv_c_va_copy" = "yes"
+then
+ AC_DEFINE(HAVE_VA_COPY, 1, [Define if we have va_copy])
+fi
+AC_CACHE_CHECK([for __va_copy], ac_cv_c___va_copy,
+ AC_TRY_LINK(
+ [#include <stdarg.h>],
+ [va_list ap1, ap2;
+ __va_copy(ap1,ap2);
+ ],
+ [ac_cv_c___va_copy="yes"],
+ [ac_cv_c___va_copy="no"])
+ )
+if test "$ac_cv_c___va_copy" = "yes"
+then
+ AC_DEFINE(HAVE___VA_COPY, 1, [Define if we have __va_copy])
+fi
+
dnl **** Check for IPX (currently Linux only) ****
AC_CACHE_CHECK([for GNU style IPX support], ac_cv_c_ipx_gnu,
AC_TRY_COMPILE(
