diff --git a/notebooks/outlier_detection.ipynb b/notebooks/outlier_detection.ipynb
index a905d30..3d38b6b 100644
--- a/notebooks/outlier_detection.ipynb
+++ b/notebooks/outlier_detection.ipynb
@@ -243,7 +243,7 @@
     "    ax1.axhline(res_std * i, ls=\":\", c=\"C{}\".format(i), label=\"{} sigma\".format(i))\n",
     "    ax1.axhline(-res_std * i, ls=\":\", c=\"C{}\".format(i))\n",
     "\n",
-    "mask2 = utils.outlier_sigma_diff(res, yerr, std_err)\n",
+    "mask = utils.outlier_sigma_diff(res, yerr, std_err)\n",
     "ax1.scatter(x[mask], res[mask], edgecolor=\"r\", facecolor=\"none\", marker=\"o\", zorder=3)\n",
     "\n",
     "ax1.invert_yaxis()\n",