diff --git a/lib/classes/GraphStream.ts b/lib/classes/GraphStream.ts
index 159130b..1f0cb11 100644
--- a/lib/classes/GraphStream.ts
+++ b/lib/classes/GraphStream.ts
@@ -52,6 +52,7 @@ export class GraphStream extends Transform {
     if (!states.includes (this._state)) {
       throw new Error (`invalid state to execute command ${instr}
   expected: ${states.join (', ')}`);
+  actual: ${this._state}`);
     }
   }