diff --git a/package/openntpd/openntpd.mk b/package/openntpd/openntpd.mk
index d51f902f03..40bb1bf7e0 100644
--- a/package/openntpd/openntpd.mk
+++ b/package/openntpd/openntpd.mk
@@ -9,6 +9,10 @@ OPENNTPD_SITE = http://ftp.openbsd.org/pub/OpenBSD/OpenNTPD
 OPENNTPD_LICENSE = MIT-like, BSD-2c, BSD-3c
 OPENNTPD_LICENSE_FILES = COPYING
 
+# openntpd uses pthread functions for arc4random emulation but forgets
+# to use -pthread
+OPENNTPD_CONF_ENV += CFLAGS="$(TARGET_CFLAGS) -pthread"
+
 define OPENNTPD_INSTALL_INIT_SYSTEMD
 	$(INSTALL) -D -m 0644 package/openntpd/ntpd.service \
 		$(TARGET_DIR)/usr/lib/systemd/system/ntpd.service