diff --git a/pyproject.toml b/pyproject.toml
index 68b19ec..1e2afdc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -132,7 +132,7 @@ optional-dependencies.doc = [
   "sphinx-autobuild==2021.3.14",   # Newer versions stopped "watching" appropriately?
   "sphinx-copybutton",
   "sphinx-design-elements<1",
-  "sphinxcontrib-mermaid<2",
+  "sphinxcontrib-mermaid<3",
   "sphinxext-opengraph<1",
 ]
 optional-dependencies.mongodb = [