diff --git a/package/uacme/uacme.mk b/package/uacme/uacme.mk
index 999cc365e9..d3d692b1f8 100644
--- a/package/uacme/uacme.mk
+++ b/package/uacme/uacme.mk
@@ -13,6 +13,8 @@ UACME_LICENSE = GPL-3.0+
 UACME_LICENSE_FILES = COPYING
 UACME_DEPENDENCIES = libcurl
 
+UACME_CONF_ENV = ac_cv_prog_cc_c99='-std=gnu99'
+
 ifeq ($(BR2_PACKAGE_MBEDTLS),y)
 UACME_CONF_OPTS += --with-mbedtls
 UACME_DEPENDENCIES += mbedtls