diff --git a/logstash-core/logstash-core.gemspec b/logstash-core/logstash-core.gemspec
index 7027bc25cde..8ad77283242 100644
--- a/logstash-core/logstash-core.gemspec
+++ b/logstash-core/logstash-core.gemspec
@@ -55,7 +55,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency "concurrent-ruby", "~> 1"
   gem.add_runtime_dependency "rack", '~> 2'
   gem.add_runtime_dependency "mustermann", '~> 1.0.3'
-  gem.add_runtime_dependency "sinatra", '~> 2'
+  gem.add_runtime_dependency "sinatra", '~> 2.1.0' # pinned until GH-13777 is resolved
   gem.add_runtime_dependency 'puma', '~> 5'
   gem.add_runtime_dependency "jruby-openssl", "~> 0.11"