diff --git a/Gemfile b/Gemfile
index 9d038fb..71dba71 100644
--- a/Gemfile
+++ b/Gemfile
@@ -43,8 +43,9 @@ gem 'rbnacl'
 gem 'slack-notifier', '~> 2.3', '>= 2.3.2'
 
 # Local previewing
-gem 'sass-embedded', '~> 1.58'
-gem 'sinatra', '~> 3'
+gem 'rackup'
+gem 'sass-embedded'
+gem 'sinatra', '~> 4'
 gem 'thin'
 
 # Pinning google-protobuf so that it continues to build on ARM devices
diff --git a/Gemfile.lock b/Gemfile.lock
index e75a258..6775ad0 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -139,14 +139,19 @@ GEM
       method_source (~> 1.0)
     public_suffix (5.0.4)
     racc (1.7.3)
-    rack (2.2.8.1)
-    rack-livereload (0.5.2)
-      rack (< 3)
-    rack-protection (3.2.0)
+    rack (3.0.9.1)
+    rack-livereload (0.5.1)
+      rack
+    rack-protection (4.0.0)
       base64 (>= 0.1.0)
-      rack (~> 2.2, >= 2.2.4)
+      rack (>= 3.0.0, < 4)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
     rack-test (2.1.0)
       rack (>= 1.3)
+    rackup (2.1.0)
+      rack (>= 3)
+      webrick (~> 1.8)
     rainbow (3.1.1)
     rake (13.1.0)
     rb-fsevent (0.11.2)
@@ -182,10 +187,11 @@ GEM
       addressable (>= 2.3.5)
       faraday (>= 0.17.3, < 3)
     shellany (0.0.1)
-    sinatra (3.2.0)
+    sinatra (4.0.0)
       mustermann (~> 3.0)
-      rack (~> 2.2, >= 2.2.4)
-      rack-protection (= 3.2.0)
+      rack (>= 3.0.0, < 4)
+      rack-protection (= 4.0.0)
+      rack-session (>= 2.0.0, < 3)
       tilt (~> 2.0)
     slack-notifier (2.4.0)
     solargraph (0.50.0)
@@ -204,10 +210,10 @@ GEM
       thor (~> 1.0)
       tilt (~> 2.0)
       yard (~> 0.9, >= 0.9.24)
-    thin (1.8.2)
-      daemons (~> 1.0, >= 1.0.9)
-      eventmachine (~> 1.0, >= 1.0.4)
-      rack (>= 1, < 3)
+    thin (1.6.2)
+      daemons (>= 1.0.9)
+      eventmachine (>= 1.0.0)
+      rack (>= 1.0.0)
     thor (1.3.1)
     tilt (2.3.0)
     tzinfo (2.0.6)
@@ -243,10 +249,11 @@ DEPENDENCIES
   octokit (~> 8)
   rack-livereload
   rack-test
+  rackup
   rbnacl
   rubocop (~> 1.0)
-  sass-embedded (~> 1.58)
-  sinatra (~> 3)
+  sass-embedded
+  sinatra (~> 4)
   slack-notifier (~> 2.3, >= 2.3.2)
   solargraph (~> 0.39)
   thin