diff --git a/configure.ac b/configure.ac
index e098758..1255db9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -26,7 +26,7 @@ AC_TYPE_SIZE_T
 # Checks for library functions.
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
-AC_CHECK_FUNCS([memset])
+AC_CHECK_FUNCS([memset letoh32 htole32])
 
 AC_CHECK_HEADERS([endian.h sys/endian.h])
 if test $ac_cv_header_endian_h = "no" -a $ac_cv_header_sys_endian_h = "no"; then