diff --git a/Gemfile b/Gemfile
index 7b9eee7..a071ba8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.3'
 # Use sqlite3 as the database for Active Record
 gem "sqlite3", git: "https://github.com/stomar/sqlite3-ruby", branch: "add-dlfcn"
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/Gemfile.lock b/Gemfile.lock
index b7a14e2..8477915 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,3 +1,10 @@
+GIT
+  remote: https://github.com/stomar/sqlite3-ruby
+  revision: 30c93813228db0fd34b9cf5809ed8609c2535b29
+  branch: add-dlfcn
+  specs:
+    sqlite3 (1.3.13.20180326210955)
+
 GEM
   remote: https://rubygems.org/
   specs:
@@ -64,6 +71,7 @@ GEM
     crass (1.0.4)
     erubi (1.7.1)
     execjs (2.7.0)
+    ffi (1.9.25)
     ffi (1.9.25-x86-mingw32)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
@@ -83,10 +91,13 @@ GEM
     minitest (5.11.3)
     multi_json (1.13.1)
     nio4r (2.3.1)
+    nokogiri (1.8.5)
+      mini_portile2 (~> 2.3.0)
     nokogiri (1.8.5-x86-mingw32)
       mini_portile2 (~> 2.3.0)
     public_suffix (3.0.3)
-    puma (3.12.0)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.6)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -139,7 +150,6 @@ GEM
       actionpack (>= 4.0)
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
-    sqlite3 (1.3.13-x86-mingw32)
     thor (0.20.3)
     thread_safe (0.3.6)
     tilt (2.0.9)
@@ -164,6 +174,7 @@ GEM
       nokogiri (~> 1.8)
 
 PLATFORMS
+  ruby
   x86-mingw32
 
 DEPENDENCIES
@@ -171,11 +182,11 @@ DEPENDENCIES
   capybara (~> 2.13)
   coffee-rails (~> 4.2)
   jbuilder (~> 2.5)
-  puma (~> 3.7)
+  puma (~> 4.3)
   rails (~> 5.1.3)
   sass-rails (~> 5.0)
   selenium-webdriver
-  sqlite3
+  sqlite3!
   turbolinks (~> 5)
   tzinfo-data
   uglifier (>= 1.3.0)