diff --git a/3. NumPy exercises.ipynb b/3. NumPy exercises.ipynb
index deff2a9..e6341c2 100644
--- a/3. NumPy exercises.ipynb	
+++ b/3. NumPy exercises.ipynb	
@@ -1366,7 +1366,7 @@
    "source": [
     "X = np.array([-1, 2, 0, -4, 5, 6, 0, 0, -9, 10])\n",
     "\n",
-    "mask = X <= 0\n",
+    "mask = X < 0\n",
     "X[mask]"
    ]
   },