diff --git a/Gemfile.lock b/Gemfile.lock
index 0c0d6410..be144546 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -14,7 +14,7 @@ PATH
       psych (~> 4.0)
       rubyzip (~> 2.0, >= 2.0.0)
       sassc (~> 2.4)
-      sinatra (~> 2.0, >= 2.0.8.1)
+      sinatra (>= 2.0.8.1, < 4)
       sinatra-contrib (~> 2.0, >= 2.0.8.1)
       systemu (~> 2.6, >= 2.6.5)
       termcolorlight (~> 1.0, >= 1.1.1)
@@ -55,7 +55,7 @@ GEM
     mime-types-data (3.2021.0704)
     minitest (5.14.4)
     multi_json (1.15.0)
-    mustermann (1.1.1)
+    mustermann (2.0.2)
       ruby2_keywords (~> 0.0.1)
     open_uri_redirections (0.2.1)
     pony (1.13.1)
@@ -73,8 +73,8 @@ GEM
     psych (4.0.1)
     psych (4.0.1-java)
       jar-dependencies (>= 0.1.7)
-    rack (2.2.3.1)
-    rack-protection (2.2.0)
+    rack (2.2.6.4)
+    rack-protection (2.2.4)
       rack
     rspec (3.10.0)
       rspec-core (~> 3.10.0)
@@ -103,23 +103,23 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.2)
-    sinatra (2.2.0)
-      mustermann (~> 1.0)
+    sinatra (2.2.4)
+      mustermann (~> 2.0)
       rack (~> 2.2)
-      rack-protection (= 2.2.0)
+      rack-protection (= 2.2.4)
       tilt (~> 2.0)
-    sinatra-contrib (2.2.0)
+    sinatra-contrib (2.2.4)
       multi_json
-      mustermann (~> 1.0)
-      rack-protection (= 2.2.0)
-      sinatra (= 2.2.0)
+      mustermann (~> 2.0)
+      rack-protection (= 2.2.4)
+      sinatra (= 2.2.4)
       tilt (~> 2.0)
     spoon (0.0.6)
       ffi
     systemu (2.6.5)
     temple (0.8.2)
     termcolorlight (1.1.1)
-    tilt (2.0.10)
+    tilt (2.1.0)
     timecop (0.9.2)
     tzinfo (2.0.4)
       concurrent-ruby (~> 1.0)
diff --git a/narou.gemspec b/narou.gemspec
index 0c10af33..fa277c6e 100644
--- a/narou.gemspec
+++ b/narou.gemspec
@@ -51,7 +51,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency 'mail', '~> 2.6.0', '>= 2.6.6'
   gem.add_runtime_dependency 'pony', '~> 1', '>= 1.11'
   gem.add_runtime_dependency 'diff-lcs', '~> 1.2', '>= 1.2.5'
-  gem.add_runtime_dependency 'sinatra', '~> 2.0', '>= 2.0.8.1'
+  gem.add_runtime_dependency 'sinatra', '>= 2.0.8.1', '< 4'
   gem.add_runtime_dependency 'sinatra-contrib', '~> 2.0', '>= 2.0.8.1'
   gem.add_runtime_dependency 'tilt', '~> 2.0', '>= 2.0.10'
   gem.add_runtime_dependency 'sassc', '~> 2.4'