diff --git a/dblayeroo.php b/dblayeroo.php
index 2cf2380..b420a29 100644
--- a/dblayeroo.php
+++ b/dblayeroo.php
@@ -1562,6 +1562,9 @@ class dblayeroo
       $this->displayColumn = array ();
     foreach ($columnNames as $nb => $display)
     {
+      if (! is_string ($display))
+        $this->DBException (
+          "displayAdd: The display column name #$nb is not a string");
       $display = $name = trim ($display);
       $pos = strpos ($display, "(");
       if ($pos !== false)