diff --git a/package/openswan/openswan.mk b/package/openswan/openswan.mk
index 4d82b491ec..ce5bdfbbec 100644
--- a/package/openswan/openswan.mk
+++ b/package/openswan/openswan.mk
@@ -9,7 +9,7 @@ OPENSWAN_SITE = http://download.openswan.org/openswan
 OPENSWAN_LICENSE = GPLv2+, BSD-3c
 OPENSWAN_LICENSE_FILES = COPYING LICENSE
 
-OPENSWAN_DEPENDENCIES = host-bison gmp iproute2
+OPENSWAN_DEPENDENCIES = host-bison host-flex gmp iproute2
 OPENSWAN_MAKE_OPT = ARCH=$(BR2_ARCH) CC="$(TARGET_CC)" \
 	USERCOMPILE="$(TARGET_CFLAGS) -fPIE" INC_USRLOCAL=/usr \
 	USE_KLIPS=false USE_MAST=false USE_NM=false