diff --git a/changelog.d/20241010_133336_danfuchs_mermaid_compat.md b/changelog.d/20241010_133336_danfuchs_mermaid_compat.md
new file mode 100644
index 0000000..1a33700
--- /dev/null
+++ b/changelog.d/20241010_133336_danfuchs_mermaid_compat.md
@@ -0,0 +1,4 @@
+### Bug fixes
+
+- Pin `sphinx` to < 8.1.0. [Sphinx 8.1.0](https://github.com/sphinx-doc/sphinx/compare/v8.0.2...v8.1.0) contains [a commit](https://github.com/sphinx-doc/sphinx/pull/12762/files#diff-a4c6bf1492ef480b94af82c988f64ca56fa256fab0ed043a5ad3d4043f89a645L14) that removes the `ExtensionError` export from the `sphinx.util` package. This currently breaks the [sphinxcontrib-mermaid](https://github.com/mgaitan/sphinxcontrib-mermaid) dependency.
+
diff --git a/pyproject.toml b/pyproject.toml
index b0bf7c8..7dcabfd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,7 +26,7 @@ requires-python = ">=3.11"
 dynamic = ["version"]
 dependencies = [
     "docutils>=0.20",  # solves an extra div bug with the bibliography directive
-    "Sphinx>=7",  # Consistent docutils constraint
+    "Sphinx>=7,<8.1.0",  # Consistent docutils constraint, mermaid compatibility
     "PyYAML",
     "GitPython",
     "requests",