diff --git a/scripts/copy-res.js b/scripts/copy-res.js
index e25d07fffc..d1fb49462b 100755
--- a/scripts/copy-res.js
+++ b/scripts/copy-res.js
@@ -67,6 +67,7 @@ const COPY_LIST = [
     ["node_modules/olm/olm_legacy.js", "webapp", { directwatch: 1 }],
     ["./config.json", "webapp", { directwatch: 1 }],
     ["contribute.json", "webapp"],
+    ["node_modules/matrix-react-sdk/res/decoder-ring/**", "webapp/decoder-ring"],
 ];
 
 const parseArgs = require('minimist');
diff --git a/webpack.config.js b/webpack.config.js
index 5bde203ea4..96a0ccd3dd 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -19,6 +19,8 @@ module.exports = (env, argv) => {
         // This makes the sourcemaps human readable for developers. We use eval-source-map
         // because the plain source-map devtool ruins the alignment.
         development['devtool'] = 'eval-source-map';
+    } else {
+        development['devtool'] = 'nosources-source-map';
     }
 
     // Resolve the directories for the react-sdk and js-sdk for later use. We resolve these early so we