diff --git a/04_mnist_basics.ipynb b/04_mnist_basics.ipynb
index ae9e767..aa077ae 100644
--- a/04_mnist_basics.ipynb
+++ b/04_mnist_basics.ipynb
@@ -3013,7 +3013,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "def mse(preds, targets): return ((preds-targets)**2).mean()"
+    "def mse(preds, targets): return ((preds-targets)**2).mean().sqrt()"
    ]
   },
   {