diff --git a/libs/ContentTypes/Markdown/LinkRenderer.php b/libs/ContentTypes/Markdown/LinkRenderer.php
index d8d455d..67b82c8 100644
--- a/libs/ContentTypes/Markdown/LinkRenderer.php
+++ b/libs/ContentTypes/Markdown/LinkRenderer.php
@@ -65,7 +65,7 @@ class LinkRenderer extends \League\CommonMark\Inline\Renderer\LinkRenderer
 
     protected function isExternalUrl($url)
     {
-        return preg_match('|^(?:[a-z]+:)?//|', $url) || substr($url, 0, 7) == "mailto:";
+        return preg_match('#^(?:[a-z]+:)?//|^mailto:#', $url);
     }
 
     /**
diff --git a/tests/ContentTypes/Markdown/LinkRendererTest.php b/tests/ContentTypes/Markdown/LinkRendererTest.php
index af84842..08a3dd8 100644
--- a/tests/ContentTypes/Markdown/LinkRendererTest.php
+++ b/tests/ContentTypes/Markdown/LinkRendererTest.php
@@ -51,6 +51,9 @@ class LinkRendererTest extends \PHPUnit_Framework_TestCase
             // /Content/Page
             ['<a href="../Widgets/Button.html">Link</a>', '[Link](../Widgets/Button.md)', 'Content/Page.html'],
             ['<a href="../Widgets/Button.html">Link</a>', '[Link](!Widgets/Button)', 'Content/Page.html'],
+
+            // Mailto links
+            ['<a href="mailto:me@mydomain.com" class="external">me@mydomain.com</a>', '[me@mydomain.com](mailto:me@mydomain.com)', 'Content/Page.html'],
         ];
     }