diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index 17b3ed5177bdbf..e5dec182220dd3 100755
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -443,6 +443,7 @@ def sync_default_gems(gem)
   def message_filter(repo, sha, input: ARGF)
     log = input.read
     log.delete!("\r")
+    log << "\n" if !log.end_with?("\n")
     repo_url = "https://github.com/#{repo}"
     subject, log = log.split(/\n(?:[ \t]*(?:\n|\z))/, 2)
     conv = proc do |s|