diff --git a/notebooks/beginner/strings.ipynb b/notebooks/beginner/strings.ipynb
index def3d05..b6dc04f 100644
--- a/notebooks/beginner/strings.ipynb
+++ b/notebooks/beginner/strings.ipynb
@@ -92,7 +92,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "my_string.replace('a', '?')\n",
+    "my_string = my_string.replace('a', '?')\n",
     "print(my_string)"
    ]
   },