diff --git a/scripts/validate_commit.py b/scripts/validate_commit.py
index 8804dce..564f806 100644
--- a/scripts/validate_commit.py
+++ b/scripts/validate_commit.py
@@ -12,7 +12,8 @@
 
 if is_pull_request:
     os.system('git fetch --deepen=1 --no-tags --quiet')
-    command_args = ['git', 'log', '--format=%B', '-n', '1', github['event']['after']]
+    sha = github['event'].get('after', github['event']['pull_request']['sha'])
+    command_args = ['git', 'log', '--format=%B', '-n', '1', sha]
 else:
     command_args = ['git', 'show', '-s', '--format=%s']