diff --git a/src/Libs/Synapsis.php b/src/Libs/Synapsis.php
index 9da591f..4231981 100644
--- a/src/Libs/Synapsis.php
+++ b/src/Libs/Synapsis.php
@@ -148,7 +148,7 @@ class Synapsis
             $paramType = $parameter->getType();
             if ($paramType === null) {
                 // If no type is declared, and it's not optional, we cannot resolve it.
-                throw new Exception('Untyped parameters expect at least a default value or must be optional.');
+                throw new Exception("Untyped parameter '{$parameter}' expect at least a default value or must be optional.");
             }
 
             if ($paramType->isBuiltin()) {