diff --git a/.github/workflows/forkprbuildpack.yml b/.github/workflows/forkprbuildpack.yml
index 808c226..47a418e 100644
--- a/.github/workflows/forkprbuildpack.yml
+++ b/.github/workflows/forkprbuildpack.yml
@@ -11,7 +11,7 @@ on:
 
 # if a second commit is pushed quickly after the first, cancel the first one's build
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.head_ref }}
   cancel-in-progress: true
 
 permissions: