diff --git a/History.md b/History.md
index 8e2f1e4e37..b0dfc2a8f8 100644
--- a/History.md
+++ b/History.md
@@ -9,6 +9,7 @@
   * Fix Errno::EINVAL when SSL is enabled and browser rejects cert (#1564)
   * Fix pumactl defaulting puma to development if an environment was not specified (#2035)
   * Fix closing file stream when reading pid from pidfile (#2048)
+  * Fix a typo in configuration option `--extra_runtime_dependencies` (#2050)
 
 ## 4.2.1 / 2019-10-07
 
diff --git a/lib/puma/cli.rb b/lib/puma/cli.rb
index aa940f84d5..cff30af861 100644
--- a/lib/puma/cli.rb
+++ b/lib/puma/cli.rb
@@ -162,7 +162,7 @@ def setup_options
           end
 
           o.on "--extra-runtime-dependencies GEM1,GEM2", "Defines any extra needed gems when using --prune-bundler" do |arg|
-            c.extra_runtime_dependencies arg.split(',')
+            user_config.extra_runtime_dependencies arg.split(',')
           end
 
           o.on "-q", "--quiet", "Do not log requests internally (default true)" do
diff --git a/test/test_cli.rb b/test/test_cli.rb
index 44d548051d..d49236246a 100644
--- a/test/test_cli.rb
+++ b/test/test_cli.rb
@@ -352,6 +352,14 @@ def test_load_path
     $LOAD_PATH.shift
   end
 
+  def test_extra_runtime_dependencies
+    cli = Puma::CLI.new ['--extra-runtime-dependencies', 'a,b']
+    extra_dependencies = cli.instance_variable_get(:@conf)
+                            .instance_variable_get(:@options)[:extra_runtime_dependencies]
+
+    assert_equal %w[a b], extra_dependencies
+  end
+
   def test_environment
     ENV.delete 'RACK_ENV'