diff --git a/Gemfile b/Gemfile
index ba5bd29..d5f4ecd 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,4 +4,4 @@ gem "rake"
 gem "rspec"
 gem "redis"
 gem "curb"
-gem "sinatra"
+gem "sinatra", ">= 4.0.0"
diff --git a/Gemfile.lock b/Gemfile.lock
index fd0e3a0..66da739 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,13 +1,17 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    base64 (0.2.0)
     curb (0.9.10)
     diff-lcs (1.3)
-    mustermann (1.1.1)
+    mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.3)
-    rack-protection (2.0.8.1)
-      rack
+    rack (3.0.8)
+    rack-protection (4.0.0)
+      base64 (>= 0.1.0)
+      rack (>= 3.0.0, < 4)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
     rake (13.0.1)
     redis (4.2.1)
     rspec (3.9.0)
@@ -23,13 +27,14 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.9.0)
     rspec-support (3.9.3)
-    ruby2_keywords (0.0.2)
-    sinatra (2.0.8.1)
-      mustermann (~> 1.0)
-      rack (~> 2.0)
-      rack-protection (= 2.0.8.1)
+    ruby2_keywords (0.0.5)
+    sinatra (4.0.0)
+      mustermann (~> 3.0)
+      rack (>= 3.0.0, < 4)
+      rack-protection (= 4.0.0)
+      rack-session (>= 2.0.0, < 3)
       tilt (~> 2.0)
-    tilt (2.0.10)
+    tilt (2.3.0)
 
 PLATFORMS
   ruby
@@ -39,7 +44,7 @@ DEPENDENCIES
   rake
   redis
   rspec
-  sinatra
+  sinatra (>= 4.0.0)
 
 BUNDLED WITH
    2.1.4