diff --git a/lib/shakapacker/dev_server_runner.rb b/lib/shakapacker/dev_server_runner.rb
index 4b91cdfc..5133c2b3 100644
--- a/lib/shakapacker/dev_server_runner.rb
+++ b/lib/shakapacker/dev_server_runner.rb
@@ -84,7 +84,7 @@ def execute_cmd
         end
 
         if @argv.delete("--debug-shakapacker") || @argv.delete("--debug-webpacker")
-          env["NODE_OPTIONS"] = "#{ENV["NODE_OPTIONS"]} --inspect-brk --trace-warnings"
+          env["NODE_OPTIONS"] = "#{env["NODE_OPTIONS"]} --inspect-brk --trace-warnings"
         end
 
         cmd += ["--config", @webpack_config]
diff --git a/lib/shakapacker/webpack_runner.rb b/lib/shakapacker/webpack_runner.rb
index 4848e378..08f4fae0 100644
--- a/lib/shakapacker/webpack_runner.rb
+++ b/lib/shakapacker/webpack_runner.rb
@@ -37,15 +37,15 @@ def run
       end
 
       if @argv.delete("--debug-shakapacker") || @argv.delete("--debug-webpacker")
-        env["NODE_OPTIONS"] = "#{ENV["NODE_OPTIONS"]} --inspect-brk"
+        env["NODE_OPTIONS"] = "#{env["NODE_OPTIONS"]} --inspect-brk"
       end
 
       if @argv.delete "--trace-deprecation"
-        env["NODE_OPTIONS"] = "#{ENV["NODE_OPTIONS"]} --trace-deprecation"
+        env["NODE_OPTIONS"] = "#{env["NODE_OPTIONS"]} --trace-deprecation"
       end
 
       if @argv.delete "--no-deprecation"
-        env["NODE_OPTIONS"] = "#{ENV["NODE_OPTIONS"]} --no-deprecation"
+        env["NODE_OPTIONS"] = "#{env["NODE_OPTIONS"]} --no-deprecation"
       end
 
       # Webpack commands are not compatible with --config option.