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'