diff --git a/backtrace.php b/backtrace.php
index 49addbd..c2dd8ec 100644
--- a/backtrace.php
+++ b/backtrace.php
@@ -6,9 +6,12 @@ class backtrace
 {
   /** Display the backtrace in the browser
     * use: \backtrace::show (debug_backtrace ());
+    * @param array $backtrace The backtrace to display
     */
   public static function show ($backtrace)
   {
+    if (! is_array ($backtrace))
+      throw new \Exception ("Backtrace invalid: not an array", 500);
     echo "<pre>Debug BackTrace:\n";
     foreach ($backtrace as $key=>$back)
     {