diff --git a/doc/source/algorithms/critical_curves.ipynb b/doc/source/algorithms/critical_curves.ipynb
index d6f8ae37eec4965ecf16f0a47eedb98540f3fea1..b2b5522f9b892e2b919a4df9848e7717b432da65 100644
--- a/doc/source/algorithms/critical_curves.ipynb
+++ b/doc/source/algorithms/critical_curves.ipynb
@@ -52,7 +52,7 @@
    "id": "e15eeded",
    "metadata": {},
    "source": [
-    "# Mixtures\n",
+    "## Mixtures\n",
     "\n",
     "A pure fluid has a single vapor-liquid critical point, but mixtures are different:\n",
     "\n",