diff --git a/Gemfile b/Gemfile
index 31294a7..7db8f26 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,7 +7,7 @@ gem 'json',              '~> 2.3'
 gem 'net-smtp',          '~> 0.3.3'
 gem 'passenger',         '~> 6.0'
 gem 'pony',              '~> 1.13'
-gem 'prometheus-client', '~> 2.1'
+gem 'prometheus-client', '~> 4.0'
 gem 'rack',              '~> 2.2'
 gem 'sinatra',           '~> 2.1'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index f5b5fc1..ea277da 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -28,7 +28,7 @@ GEM
       rake (>= 0.8.1)
     pony (1.13.1)
       mail (>= 2.0)
-    prometheus-client (2.1.0)
+    prometheus-client (4.0.0)
     rack (2.2.4)
     rack-protection (2.2.2)
       rack
@@ -77,7 +77,7 @@ DEPENDENCIES
   net-smtp (~> 0.3.3)
   passenger (~> 6.0)
   pony (~> 1.13)
-  prometheus-client (~> 2.1)
+  prometheus-client (~> 4.0)
   rack (~> 2.2)
   rack-test (~> 2.0)
   rubocop (~> 1.44)