diff --git a/doc/examples/monthly-means.ipynb b/doc/examples/monthly-means.ipynb
index 508575855d9..fad40e019de 100644
--- a/doc/examples/monthly-means.ipynb
+++ b/doc/examples/monthly-means.ipynb
@@ -107,7 +107,7 @@
     "    \n",
     "    for i, (month, year) in enumerate(zip(time.month, time.year)):\n",
     "        month_length[i] = cal_days[month]\n",
-    "        if leap_year(year, calendar=calendar):\n",
+    "        if leap_year(year, calendar=calendar) and month == 2:\n",
     "            month_length[i] += 1\n",
     "    return month_length"
    ]