runs builds for pull requests against branch
diff --git a/.github/workflows/mahout.yml b/.github/workflows/mahout.yml
index d3beb3b..4387a12 100644
--- a/.github/workflows/mahout.yml
+++ b/.github/workflows/mahout.yml
@@ -16,6 +16,10 @@
 name: Java CI with Maven
 
 on:
+  pull_request:
+    types: [opened]
+    branches:
+      - trunk
   push:
     branches:
       - trunk