diff --git a/CHANGES.md b/CHANGES.md
index 049dfea5..f6ca7569 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -3,7 +3,7 @@
 ## Breaking Changes
 
 - Validation of the configuration object provided by `nwb.config.js` files has been expanded, so previously valid config files may now be invalid:
-  - Unexpected properties in top-level configuration or in `babel`, `karma`, `npm` and `webpack` configuration (i.e. anything that's not documented in the [Configuration docs](https://github.com/insin/nwb/blob/master/docs/Configuration.md)) are now treated as errors.
+  - Unexpected properties in top-level configuration or in `babel`, `karma`, `npm` and `webpack` configuration (i.e. anything that's not documented in the [Configuration docs](https://github.com/insin/nwb/blob/master/docs/Configuration.md)) are now treated as errors [[#193](https://github.com/insin/nwb/issues/193)]
   - Basic type checking is now performed for all documented configuration properties.
   - After upgrading, run `nwb check-config` to check your configuration file.
 - Updated to [UglifyJSPlugin 1.x](https://github.com/webpack-contrib/uglifyjs-webpack-plugin#readme), which supports ES2015 syntax and adds options to enable filesystem caching and use multiple processes to improve build speed, which nwb enables by default [[#412](https://github.com/insin/nwb/issues/412)]
diff --git a/src/config/karma.js b/src/config/karma.js
index db7f1ab4..baf56d1b 100644
--- a/src/config/karma.js
+++ b/src/config/karma.js
@@ -24,7 +24,8 @@ export function processKarmaConfig({report, userConfig}) {
       'karma',
       unexpectedProps.join(', '),
       `Unexpected prop${s(unexpectedProps.length)} in ${chalk.cyan('karma')} config - ` +
-      'see https://github.com/insin/nwb/blob/master/docs/Configuration.md#karma-configuration for supported config'
+      'see https://github.com/insin/nwb/blob/master/docs/Configuration.md#karma-configuration for supported config.' +
+      `If you were trying to add extra Karma config, try putting it in ${chalk.cyan('karma.extra')} instead`
     )
   }
 
diff --git a/src/config/webpack.js b/src/config/webpack.js
index 81d01314..9a8ba328 100644
--- a/src/config/webpack.js
+++ b/src/config/webpack.js
@@ -38,7 +38,8 @@ export function processWebpackConfig({pluginConfig, report, userConfig}) {
       'webpack',
       unexpectedProps.join(', '),
       `Unexpected prop${s(unexpectedProps.length)} in ${chalk.cyan('webpack')} config - ` +
-      'see https://github.com/insin/nwb/blob/master/docs/Configuration.md#webpack-configuration for supported config'
+      'see https://github.com/insin/nwb/blob/master/docs/Configuration.md#webpack-configuration for supported config. ' +
+      `If you were trying to add extra Webpack config, try putting it in ${chalk.cyan('webpack.extra')} instead`
     )
   }