diff --git a/scripts/buildkite_utils.py b/scripts/buildkite_utils.py
index d4ff78f..b7b4a9c 100644
--- a/scripts/buildkite_utils.py
+++ b/scripts/buildkite_utils.py
@@ -78,6 +78,9 @@ class BuildkiteApi:
         # https://buildkite.com/docs/apis/rest-api/builds#get-a-build
         return benedict(self.get(f'https://api.buildkite.com/v2/organizations/{self.organization}/pipelines/{pipeline}/builds/{build_number}').json())
 
+    def list_running_revision_builds(self, pipeline: str, rev: str):
+        return self.get(f'https://api.buildkite.com/v2/organizations/{self.organization}/pipelines/{pipeline}/builds?state[]=scheduled&state[]=running&meta_data[ph_buildable_revision]={rev}').json()
+
     @backoff.on_exception(backoff.expo, Exception, max_tries=3, logger='', factor=3)
     def get(self, url: str):
         authorization = f'Bearer {self.token}'
@@ -86,6 +89,15 @@ class BuildkiteApi:
             raise Exception(f'Buildkite responded with non-OK status: {response.status_code}')
         return response
 
+    # cancel a build. 'build' is a json object returned by API.
+    def cancel_build(self, build):
+        build = benedict(build)
+        url = f'https://api.buildkite.com/v2/organizations/{self.organization}/pipelines/{build.get("pipeline.slug")}/builds/{build.get("number")}/cancel'
+        authorization = f'Bearer {self.token}'
+        response = requests.put(url, headers={'Authorization': authorization})
+        if response.status_code != 200:
+            raise Exception(f'Buildkite responded with non-OK status: {response.status_code}')
+
 
 def format_url(url: str, name: Optional[str] = None):
     if name is None:
diff --git a/scripts/cancel_previous_build.py b/scripts/cancel_previous_build.py
deleted file mode 100755
index 940e908..0000000
--- a/scripts/cancel_previous_build.py
+++ /dev/null
@@ -1,33 +0,0 @@
-#!/usr/bin/env python3
-# Copyright 2020 Google LLC
-#
-# Licensed under the the Apache License v2.0 with LLVM Exceptions (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     https://llvm.org/LICENSE.txt
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-import os
-import requests
-
-def main(review_number, api_key):
-    buildkite = requests.Session()
-    buildkite.headers.update({'Authorization': 'Bearer {}'.format(api_key)})
-    api = lambda query: 'https://api.buildkite.com/v2' + query
-
-    builds = buildkite.get(api('/organizations/llvm-project/builds?state[]=scheduled&state[]=running')).json()
-    for build in builds:
-        if build['message'] == review_number:
-            pipeline = build['pipeline']['slug']
-            buildkite.put(api('/organizations/llvm-project/pipelines/{}/builds/{}/cancel'.format(pipeline, build['number'])))
-
-if __name__ == '__main__':
-    review_number = 'D{}'.format(os.getenv('ph_buildable_revision'))
-    api_key = # TODO where do we get that? The agents on the service queue need to have the proper access (read_builds and write_builds)
-    main(review_number, api_key)
diff --git a/scripts/pipeline_create_branch.py b/scripts/pipeline_create_branch.py
index b04463e..a28c471 100755
--- a/scripts/pipeline_create_branch.py
+++ b/scripts/pipeline_create_branch.py
@@ -15,7 +15,9 @@
 
 import os
 import yaml
-from buildkite_utils import annotate, feedback_url, set_metadata
+import logging
+from buildkite_utils import set_metadata, BuildkiteApi
+
 
 if __name__ == '__main__':
     diff_id = os.getenv("ph_buildable_diff")
@@ -23,6 +25,17 @@ if __name__ == '__main__':
     base_commit = os.getenv('ph_base_commit', 'auto')
     run_build = os.getenv('ph_skip_build') is None
     trigger = os.getenv('ph_trigger_pipeline')
+    logging.basicConfig(level=log_level, format='%(levelname)-7s %(message)s')
+
+    # Cancel any existing builds.
+    # Do this before setting own 'ph_buildable_revision'.
+    try:
+        bk = BuildkiteApi(os.getenv("BUILDKITE_API_TOKEN"), os.getenv("BUILDKITE_ORGANIZATION_SLUG"))
+        for b in bk.list_running_revision_builds(os.getenv("BUILDKITE_PIPELINE_SLUG"), os.getenv('ph_buildable_revision')):
+            logging.info(f'cancelling build {b.get("web_url")}')
+            bk.cancel_build(b)
+    except Exception as e:
+        logging.error(e)
 
     set_metadata('ph_buildable_diff', os.getenv("ph_buildable_diff"))
     set_metadata('ph_buildable_revision', os.getenv('ph_buildable_revision'))