diff --git a/app/assets/javascripts/pretty-text/engines/discourse-markdown/bbcode.js.es6 b/app/assets/javascripts/pretty-text/engines/discourse-markdown/bbcode.js.es6
index d50880c2938..bc15c40fb2b 100644
--- a/app/assets/javascripts/pretty-text/engines/discourse-markdown/bbcode.js.es6
+++ b/app/assets/javascripts/pretty-text/engines/discourse-markdown/bbcode.js.es6
@@ -114,10 +114,12 @@ export function setup(helper) {
 
   replaceBBCode('url', contents => {
     if (!Array.isArray(contents)) { return; }
-    if (contents.length === 1 && contents[0][0] === 'a') {
+
+    const first = contents[0];
+    if (contents.length === 1 && Array.isArray(first) && first[0] === 'a') {
       // single-line bbcode links shouldn't be oneboxed, so we mark this as a bbcode link.
-      if (typeof contents[0][1] !== 'object') { contents[0].splice(1, 0, {}); }
-      contents[0][1]['data-bbcode'] = true;
+      if (typeof first[1] !== 'object') { first.splice(1, 0, {}); }
+      first[1]['data-bbcode'] = true;
     }
     return ['concat'].concat(contents);
   });
diff --git a/test/javascripts/lib/pretty-text-test.js.es6 b/test/javascripts/lib/pretty-text-test.js.es6
index e4ef370a01e..af6486b33a9 100644
--- a/test/javascripts/lib/pretty-text-test.js.es6
+++ b/test/javascripts/lib/pretty-text-test.js.es6
@@ -551,6 +551,7 @@ test('basic bbcode', function() {
 
 test('urls', function() {
   cookedPara("[url]not a url[/url]", "not a url", "supports [url] that isn't a url");
+  cookedPara("[url]abc.com[/url]", "abc.com", "no error when a url has no protocol and begins with a");
   cookedPara("[url]http://bettercallsaul.com[/url]", "<a href=\"http://bettercallsaul.com\">http://bettercallsaul.com</a>", "supports [url] without parameter");
   cookedPara("[url=http://example.com]example[/url]", "<a href=\"http://example.com\">example</a>", "supports [url] with given href");
   cookedPara("[url=http://www.example.com][img]http://example.com/logo.png[/img][/url]",