diff --git a/package/ipsec-tools/Config.in b/package/ipsec-tools/Config.in
index 964218e1c7..e7a948905e 100644
--- a/package/ipsec-tools/Config.in
+++ b/package/ipsec-tools/Config.in
@@ -2,6 +2,7 @@ config BR2_PACKAGE_IPSEC_TOOLS
 	bool "ipsec-tools"
 	default n
         select BR2_PACKAGE_OPENSSL
+	select BR2_PACKAGE_FLEX
 	help
 	  This package is required to support IPSec for Linux 2.6+