diff --git a/Gemfile.lock b/Gemfile.lock
index 33ecf0c..2b691ad 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -3,17 +3,17 @@ PATH
   specs:
     rucksack (0.1.0)
       rack (>= 2.1.4)
-      sinatra (~> 2.0)
+      sinatra (>= 2, < 4)
       zeitwerk (~> 2.2)
 
 GEM
   remote: https://rubygems.org/
   specs:
     diff-lcs (1.3)
-    mustermann (1.1.1)
+    mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.3)
-    rack-protection (2.1.0)
+    rack (2.2.4)
+    rack-protection (3.0.4)
       rack
     rake (13.0.1)
     rspec (3.9.0)
@@ -29,13 +29,13 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.9.0)
     rspec-support (3.9.0)
-    ruby2_keywords (0.0.2)
-    sinatra (2.1.0)
-      mustermann (~> 1.0)
-      rack (~> 2.2)
-      rack-protection (= 2.1.0)
+    ruby2_keywords (0.0.5)
+    sinatra (3.0.4)
+      mustermann (~> 3.0)
+      rack (~> 2.2, >= 2.2.4)
+      rack-protection (= 3.0.4)
       tilt (~> 2.0)
-    tilt (2.0.10)
+    tilt (2.0.11)
     zeitwerk (2.4.2)
 
 PLATFORMS
diff --git a/rucksack.gemspec b/rucksack.gemspec
index e17d183..54dc6f1 100644
--- a/rucksack.gemspec
+++ b/rucksack.gemspec
@@ -33,5 +33,5 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency "rack", ">= 2.1.4"
   spec.add_dependency "zeitwerk", "~> 2.2"
-  spec.add_dependency "sinatra", "~> 2.0"
+  spec.add_dependency "sinatra", ">= 2", "< 4"
 end