diff --git a/.github/workflows/api-breaking-changes.yml b/.github/workflows/api-breaking-changes.yml
index c6227792c1..fbe4764a9f 100644
--- a/.github/workflows/api-breaking-changes.yml
+++ b/.github/workflows/api-breaking-changes.yml
@@ -36,7 +36,7 @@ jobs:
 
       - name: breaking changes check
         run: |
-          yarn backstage-repo-tools repo schema openapi check > comment.md
+          yarn backstage-repo-tools repo schema openapi check --since ${{ github.base_ref }} > comment.md
 
       - name: Upload Rendered Comment as Artifact
         uses: actions/upload-artifact@a8a3f3ad30e3422c9c7b888a15615d19a852ae32 # v3
diff --git a/packages/repo-tools/src/commands/repo/schema/openapi/check.ts b/packages/repo-tools/src/commands/repo/schema/openapi/check.ts
index 41d0bec0e5..492dd3b5be 100644
--- a/packages/repo-tools/src/commands/repo/schema/openapi/check.ts
+++ b/packages/repo-tools/src/commands/repo/schema/openapi/check.ts
@@ -47,7 +47,7 @@ export async function command(opts: OptionValues) {
       severity: 0,
     } as CiRunDetails;
     for (const pkg of checkablePackages) {
-      const baseRef = opts.since ?? process.env.GITHUB_BASE_REF;
+      const baseRef = opts.since;
       const { stdout } = await exec(
         'yarn',
         ['check:api', '--ignore', '--json', '--since', baseRef],