diff --git a/15_processing_sequences_using_rnns_and_cnns.ipynb b/15_processing_sequences_using_rnns_and_cnns.ipynb
index 137342f..e530c36 100644
--- a/15_processing_sequences_using_rnns_and_cnns.ipynb
+++ b/15_processing_sequences_using_rnns_and_cnns.ipynb
@@ -583,7 +583,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "Y_naive_pred = Y_valid[:, -1:]\n",
+    "Y_naive_pred = np.tile(X_valid[:, -1], 10) # take the last time step value, and repeat it 10 times\n",
     "np.mean(keras.metrics.mean_squared_error(Y_valid, Y_naive_pred))"
    ]
   },