diff --git a/extensions/chromium/pdfHandler.js b/extensions/chromium/pdfHandler.js
index 905d51fa1..0eba4e34b 100644
--- a/extensions/chromium/pdfHandler.js
+++ b/extensions/chromium/pdfHandler.js
@@ -153,10 +153,16 @@ chrome.webRequest.onBeforeRequest.addListener(
     urls: [
       'file://*/*.pdf',
       'file://*/*.PDF',
-      // Note: Chrome 59 has disabled ftp resource loading by default:
-      // https://www.chromestatus.com/feature/5709390967472128
-      'ftp://*/*.pdf',
-      'ftp://*/*.PDF',
+      ...(
+        // Duck-typing: MediaError.prototype.message was added in Chrome 59.
+        MediaError.prototype.hasOwnProperty('message') ? [] :
+        [
+          // Note: Chrome 59 has disabled ftp resource loading by default:
+          // https://www.chromestatus.com/feature/5709390967472128
+          'ftp://*/*.pdf',
+          'ftp://*/*.PDF',
+        ]
+      ),
     ],
     types: ['main_frame', 'sub_frame'],
   },