diff --git a/appveyor.yml b/appveyor.yml
index 3df8ed4ef6..addd2632e0 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -63,7 +63,7 @@ install:
   - has-env GH
   # clean cache to prevent install permission issues
   - yarn cache clean
-  - yarn || yarn || yarn
+  - yarn --frozen-lockfile || yarn --frozen-lockfile || yarn --frozen-lockfile
   - .\node_modules\.bin\print-arch
 
 # Post-install test scripts.
diff --git a/circle.yml b/circle.yml
index 55b4cfc96a..a201a95bda 100644
--- a/circle.yml
+++ b/circle.yml
@@ -236,7 +236,7 @@ jobs:
       - run: ls $(yarn global bin)/../lib/node_modules
 
       # try several times, because flaky NPM installs ...
-      - run: yarn || yarn
+      - run: yarn --frozen-lockfile || yarn --frozen-lockfile
       - run:
           name: Top level packages
           command: yarn list --depth=0 || true