diff --git a/workflow/notebooks/plot-precision-recall.py.ipynb b/workflow/notebooks/plot-precision-recall.py.ipynb
index f5f4169..c672a2c 100644
--- a/workflow/notebooks/plot-precision-recall.py.ipynb
+++ b/workflow/notebooks/plot-precision-recall.py.ipynb
@@ -119,7 +119,7 @@
     "    report[\"coverage\"] = report[\"coverage\"].apply(lambda cov: snakemake.params.cov_labels[cov])\n",
     "\n",
     "    report[\"tp_no_gt\"] = report[\"QUERY.TOTAL\"] - report[\"QUERY.FP\"] + report[\"FP.gt\"]\n",
-    "    report[\"t\"] = report[\"tp_no_gt\"] + report[\"TRUTH.FN\"]\n",
+    "    report[\"t\"] = report[\"tp_no_gt\"] + report[\"TRUTH.FN\"] - report[\"FP.gt\"] # TRUTH.FN alone also counts mismatched genotypes.\n",
     "    report[\"precision\"] = report[\"tp_no_gt\"] / report[\"QUERY.TOTAL\"]\n",
     "    report[\"recall\"] = report[\"tp_no_gt\"] / (report[\"t\"])\n",
     "    report[\"correct genotype\"] = \"no\"\n",