diff --git a/2 - Pandas Series exercises.ipynb b/2 - Pandas Series exercises.ipynb
index 4213ac6..5b84e84 100644
--- a/2 - Pandas Series exercises.ipynb	
+++ b/2 - Pandas Series exercises.ipynb	
@@ -642,7 +642,7 @@
    "source": [
     "X = pd.Series([-1,2,0,-4,5,6,0,0,-9,10])\n",
     "\n",
-    "mask = X <= 0\n",
+    "mask = X < 0\n",
     "X[mask]"
    ]
   },