diff --git a/bin/webpack-dev-server.js b/bin/webpack-dev-server.js
index d58daf2954..b491cca980 100755
--- a/bin/webpack-dev-server.js
+++ b/bin/webpack-dev-server.js
@@ -113,6 +113,9 @@ function processOptions (config) {
     ? config[0]
     : config;
 
+  // This updates both config and firstWpOpt
+  firstWpOpt.mode = defaultTo(firstWpOpt.mode, 'development');
+
   const options = config.devServer || firstWpOpt.devServer || {};
 
   if (argv.bonjour) {