diff --git a/History.md b/History.md
index ac19397778..9d97029275 100644
--- a/History.md
+++ b/History.md
@@ -6,6 +6,7 @@
 
 * Bugfixes
   * Cleanup daemonization in rc.d script (#2409)
+  * Fix `Bundler::GemNotFound` errors for `nio4r` gem during phased restarts (#2427)
   * Fire `on_booted` after server starts
 
 * Refactor
diff --git a/bin/puma-wild b/bin/puma-wild
index b3ba0152e3..5db409f795 100644
--- a/bin/puma-wild
+++ b/bin/puma-wild
@@ -5,24 +5,18 @@
 
 require 'rubygems'
 
-gems = ARGV.shift
+cli_arg = ARGV.shift
 
 inc = ""
 
-if gems == "-I"
+if cli_arg == "-I"
   inc = ARGV.shift
   $LOAD_PATH.concat inc.split(":")
-  gems = ARGV.shift
-end
-
-gems.split(",").each do |s|
-  name, ver = s.split(":",2)
-  gem name, ver
 end
 
 module Puma; end
 
-Puma.const_set("WILD_ARGS", ["-I", inc, gems])
+Puma.const_set("WILD_ARGS", ["-I", inc])
 
 require 'puma/cli'
 
diff --git a/lib/puma/launcher.rb b/lib/puma/launcher.rb
index 06ae028412..c8811b975a 100644
--- a/lib/puma/launcher.rb
+++ b/lib/puma/launcher.rb
@@ -264,15 +264,11 @@ def restart!
       end
     end
 
-    # @!attribute [r] dependencies_and_files_to_require_after_prune
-    def dependencies_and_files_to_require_after_prune
+    # @!attribute [r] files_to_require_after_prune
+    def files_to_require_after_prune
       puma = spec_for_gem("puma")
 
-      deps = puma.runtime_dependencies.map do |d|
-        "#{d.name}:#{spec_for_gem(d.name).version}"
-      end
-
-      [deps, require_paths_for_gem(puma) + extra_runtime_deps_directories]
+      require_paths_for_gem(puma) + extra_runtime_deps_directories
     end
 
     # @!attribute [r] extra_runtime_deps_directories
@@ -304,7 +300,7 @@ def prune_bundler
         return
       end
 
-      deps, dirs = dependencies_and_files_to_require_after_prune
+      dirs = files_to_require_after_prune
 
       log '* Pruning Bundler environment'
       home = ENV['GEM_HOME']
@@ -313,7 +309,7 @@ def prune_bundler
         ENV['GEM_HOME'] = home
         ENV['BUNDLE_GEMFILE'] = bundle_gemfile
         ENV['PUMA_BUNDLER_PRUNED'] = '1'
-        args = [Gem.ruby, puma_wild_location, '-I', dirs.join(':'), deps.join(',')] + @original_argv
+        args = [Gem.ruby, puma_wild_location, '-I', dirs.join(':')] + @original_argv
         # Ruby 2.0+ defaults to true which breaks socket activation
         args += [{:close_others => false}]
         Kernel.exec(*args)
diff --git a/lib/puma/reactor.rb b/lib/puma/reactor.rb
index 520cfc0e53..89517270e5 100644
--- a/lib/puma/reactor.rb
+++ b/lib/puma/reactor.rb
@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 
-require 'nio'
 require 'puma/queue_close' if RUBY_VERSION < '2.3'
 
 module Puma
@@ -20,6 +19,7 @@ class Reactor
     # The provided block will be invoked when an IO has data available to read,
     # its timeout elapses, or when the Reactor shuts down.
     def initialize(&block)
+      require 'nio'
       @selector = NIO::Selector.new
       @input = Queue.new
       @timeouts = []
diff --git a/test/config/prune_bundler_with_deps.rb b/test/config/prune_bundler_with_deps.rb
index 57fe7cba65..5c5675bd4d 100644
--- a/test/config/prune_bundler_with_deps.rb
+++ b/test/config/prune_bundler_with_deps.rb
@@ -1,2 +1,7 @@
 prune_bundler true
 extra_runtime_dependencies ["rdoc"]
+before_fork do
+  $LOAD_PATH.each do |path|
+    puts "LOAD_PATH: #{path}"
+  end
+end
diff --git a/test/rackup/hello-last-load-path.ru b/test/rackup/hello-last-load-path.ru
deleted file mode 100644
index aea0c6b942..0000000000
--- a/test/rackup/hello-last-load-path.ru
+++ /dev/null
@@ -1,3 +0,0 @@
-run lambda { |env|
-  [200, {}, [$LOAD_PATH[-1]]]
-}
diff --git a/test/test_integration_cluster.rb b/test/test_integration_cluster.rb
index aa8c35374b..50700ab864 100644
--- a/test/test_integration_cluster.rb
+++ b/test/test_integration_cluster.rb
@@ -239,10 +239,26 @@ def test_prune_bundler_with_multiple_workers
   end
 
   def test_load_path_includes_extra_deps
-    cli_server "-w #{workers} -C test/config/prune_bundler_with_deps.rb test/rackup/hello-last-load-path.ru"
-    last_load_path = read_body(connect)
+    cli_server "-w #{workers} -C test/config/prune_bundler_with_deps.rb test/rackup/hello.ru"
 
-    assert_match(%r{gems/rdoc-[\d.]+/lib$}, last_load_path)
+    load_path = []
+    while (line = @server.gets) =~ /^LOAD_PATH/
+      load_path << line.gsub(/^LOAD_PATH: /, '')
+    end
+    assert_match(%r{gems/rdoc-[\d.]+/lib$}, load_path.last)
+  end
+
+  def test_load_path_does_not_include_nio4r
+    cli_server "-w #{workers} -C test/config/prune_bundler_with_deps.rb test/rackup/hello.ru"
+
+    load_path = []
+    while (line = @server.gets) =~ /^LOAD_PATH/
+      load_path << line.gsub(/^LOAD_PATH: /, '')
+    end
+
+    load_path.each do |path|
+      refute_match(%r{gems/nio4r-[\d.]+/lib}, path)
+    end
   end
 
   private
diff --git a/test/test_launcher.rb b/test/test_launcher.rb
index 815a1aeada..de145d9c00 100644
--- a/test/test_launcher.rb
+++ b/test/test_launcher.rb
@@ -7,29 +7,25 @@
 class TestLauncher < Minitest::Test
   include TmpPath
 
-  def test_dependencies_and_files_to_require_after_prune_is_correctly_built_for_no_extra_deps
+  def test_files_to_require_after_prune_is_correctly_built_for_no_extra_deps
     skip_on :no_bundler
 
-    deps, dirs = launcher.send(:dependencies_and_files_to_require_after_prune)
+    dirs = launcher.send(:files_to_require_after_prune)
 
-    assert_equal(1, deps.length)
-    assert_match(%r{^nio4r:[\d.]+$}, deps.first)
     assert_equal(2, dirs.length)
     assert_match(%r{puma/lib$}, dirs[0]) # lib dir
     assert_match(%r{puma-#{Puma::Const::PUMA_VERSION}$}, dirs[1]) # native extension dir
     refute_match(%r{gems/rdoc-[\d.]+/lib$}, dirs[2])
   end
 
-  def test_dependencies_and_files_to_require_after_prune_is_correctly_built_with_extra_deps
+  def test_files_to_require_after_prune_is_correctly_built_with_extra_deps
     skip_on :no_bundler
     conf = Puma::Configuration.new do |c|
       c.extra_runtime_dependencies ['rdoc']
     end
 
-    deps, dirs = launcher(conf).send(:dependencies_and_files_to_require_after_prune)
+    dirs = launcher(conf).send(:files_to_require_after_prune)
 
-    assert_equal(1, deps.length)
-    assert_match(%r{^nio4r:[\d.]+$}, deps.first)
     assert_equal(3, dirs.length)
     assert_match(%r{puma/lib$}, dirs[0]) # lib dir
     assert_match(%r{puma-#{Puma::Const::PUMA_VERSION}$}, dirs[1]) # native extension dir