diff --git a/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php b/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
--- a/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
+++ b/src/markup/engine/remarkup/markuprule/PhutilRemarkupDocumentLinkRule.php
@@ -102,6 +102,10 @@
   public function markupAlternateLink(array $matches) {
     $uri = trim($matches[2]);
 
+    if (!strlen($uri)) {
+      return $matches[0];
+    }
+
     // NOTE: We apply some special rules to avoid false positives here. The
     // major concern is that we do not want to convert `x[0][1](y)` in a
     // discussion about C source code into a link. To this end, we:
@@ -114,10 +118,6 @@
       return $matches[0];
     }
 
-    if (!strlen($uri[0])) {
-      return $matches[0];
-    }
-
     if (strpos($uri, '/') === false &&
         strpos($uri, '@') === false &&
         strncmp($uri, 'tel:', 4)) {