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