diff --git a/requirements.txt b/requirements.txt
index 382f5a5..edd788c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ pre-commit
 pydata-sphinx-theme
 sphinx>=7
 sphinx-design
+sphinx-notfound-page
diff --git a/src/404.md b/src/404.md
new file mode 100644
index 0000000..d1c9cf3
--- /dev/null
+++ b/src/404.md
@@ -0,0 +1,10 @@
+---
+orphan: true
+permalink: /404.html
+---
+
+# Page not found
+
+**Sorry, this page couldn't be found.**
+
+Click on the navigation bar at the top of the page to go elsewhere.
diff --git a/src/conf.py b/src/conf.py
index e2127cb..546f10d 100644
--- a/src/conf.py
+++ b/src/conf.py
@@ -25,6 +25,7 @@
 extensions = [
     "myst_parser",
     "sphinx_design",
+    "notfound.extension",
 ]
 
 myst_enable_extensions = [
@@ -67,6 +68,8 @@
 
 html_static_path = ["_static"]
 
+notfound_urls_prefix = ''
+
 
 def setup(app):
     # Styles applied to the entire wiki