diff --git a/Dockerfile b/Dockerfile
index 06ed978..db06d6f 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@ RUN mkdir -p /code
 WORKDIR /code
 
 # Install global and local dependencies first so they can be cached.
-RUN npm install -g yarn@^1.17
+RUN npm install -gf yarn@^1.21.1
 COPY package.json yarn.lock /code/
 RUN yarn