diff --git a/package/ucl/ucl.mk b/package/ucl/ucl.mk
index 2654a5a7ca..e4dc1b3eda 100644
--- a/package/ucl/ucl.mk
+++ b/package/ucl/ucl.mk
@@ -9,4 +9,7 @@ UCL_SITE = http://www.oberhumer.com/opensource/ucl/download
 UCL_LICENSE = GPLv2+
 UCL_LICENSE_FILES = COPYING
 
+# Fix ACC conformance test failure for host gcc 6.x
+HOST_UCL_CONF_ENV += CPPFLAGS="$(HOST_CPPFLAGS) -std=c90"
+
 $(eval $(host-autotools-package))