diff --git a/MD_STD_IN.php b/MD_STD_IN.php
index b3dc315..e1a82c5 100644
--- a/MD_STD_IN.php
+++ b/MD_STD_IN.php
@@ -107,7 +107,7 @@ final class MD_STD_IN {
         else $output = self::sanitize_text($default);
 
         if (!empty($allowed) and !\in_array($output, $allowed, true)) {
-            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: " . implode(', ', $allowed));
+            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: '" . implode('\', \'', $allowed) . "'");
         }
 
         return $output;
@@ -132,7 +132,7 @@ final class MD_STD_IN {
         else $output = self::sanitize_text($default);
 
         if (!empty($allowed) and !\in_array($output, $allowed, true)) {
-            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: " . implode(', ', $allowed));
+            Throw new MDpageParameterNotFromListException("Parameter `{$var_name}` must be any of the allowed values: '" . implode('\', \'', $allowed) . "'");
         }
 
         return $output;