diff --git a/build/docker/ubuntu-xenial/Dockerfile b/build/docker/ubuntu-xenial/Dockerfile
index 88895a0..5693a2c 100644
--- a/build/docker/ubuntu-xenial/Dockerfile
+++ b/build/docker/ubuntu-xenial/Dockerfile
@@ -218,6 +218,7 @@
       php7.0 \
       php7.0-cli \
       php7.0-dev \
+      php-json \
       php-pear \
       re2c \
       composer