diff --git a/includes/common.inc b/includes/common.inc
index 0ff70c9..e833ad2 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -723,6 +723,12 @@ function _external_url_is_local($url) {
     $url_parts['path'] = '/';
   }
 
+  // Force the external path to have a trailing slash for the comparison below,
+  // since base_path() always has one.
+  if (substr($url_parts['path'], -1) != '/') {
+    $url_parts['path'] .= '/';
+  }
+
   // When comparing base paths, we need a trailing slash to make sure a
   // partial URL match isn't occuring. Since base_path() always returns with
   // a trailing slash, we don't need to add the trailing slash here.