diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index f1da30a13..04fbd2733 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -9,6 +9,9 @@ on:
       - trying
       # Build the master branch.
       - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
   test: