diff --git a/getopts.php b/getopts.php
index 18cd6df..468683d 100644
--- a/getopts.php
+++ b/getopts.php
@@ -316,9 +316,9 @@ class getopts
               if (array_key_exists ($pos+1, $tokens) &&
                   $tokens[$pos+1] === "--" &&
                   ! array_key_exists ($pos+2, $tokens))
-                throw new \Exception (dgettext ("domframework",
-                  "Mandatory value for parameter '$opt' is not provided ".
-                  "after double-dash"), 500);
+                throw new \Exception (sprintf (dgettext ("domframework",
+        "Mandatory value for parameter '%s' is not provided after double-dash"),
+                $opt), 500);
               if (! array_key_exists ($pos+1, $tokens) ||
                   substr ($tokens[$pos+1], 0, 1) === "-")
                 throw new \Exception (dgettext ("domframework",