diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index eb92a02c..8c297dbc 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -7,6 +7,10 @@
     "message": "Add Style",
     "description": "Title of the page for adding styles"
   },
+  "alphaChannel": {
+    "message": "Alpha channel",
+    "description": "Label of alpha channel input"
+  },
   "appliesAdd": {
     "message": "Add",
     "description": "Label for the button to add an 'applies' entry"
diff --git a/manage/config-dialog.js b/manage/config-dialog.js
index 6386629c..82e0a38f 100644
--- a/manage/config-dialog.js
+++ b/manage/config-dialog.js
@@ -33,8 +33,14 @@ function configDialog(style) {
       let appendChild;
       if (va.type === 'color') {
         va.inputColor = $element({tag: 'input', type: 'color'});
-        // FIXME: i18n
-        va.inputAlpha = $element({tag: 'input', type: 'range', min: 0, max: 1, title: 'Opacity', step: 'any'});
+        va.inputAlpha = $element({
+          tag: 'input',
+          type: 'range',
+          min: 0,
+          max: 1,
+          title: chrome.i18n.getMessage('alphaChannel'),
+          step: 'any'
+        });
         va.inputColor.onchange = va.inputAlpha.oninput = () => {
           va.dirty = true;
           const color = colorParser.parse(va.inputColor.value);