diff --git a/configure.ac b/configure.ac
index d171b88e..4b526c0c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -660,6 +660,8 @@ AC_SUBST([OPTIONAL_ZLIB_CFLAGS])
 AC_SUBST([OPTIONAL_ZLIB_LIBS])
 AC_SUBST([OPTIONAL_READLINE_CFLAGS])
 AC_SUBST([OPTIONAL_READLINE_LIBS])
+AC_SUBST([OPTIONAL_ICONV_CFLAGS])
+AC_SUBST([OPTIONAL_ICONV_LIBS])
 AC_SUBST([OPTIONAL_OPENSSL_CFLAGS])
 AC_SUBST([OPTIONAL_OPENSSL_LIBS])
 AC_SUBST([OPTIONAL_OPENCT_CFLAGS])