diff --git a/app.py b/app.py
index 488ea463..718190bb 100644
--- a/app.py
+++ b/app.py
@@ -2,7 +2,7 @@
 
 import os
 
-from flask import Flask, abort, send_from_directory
+from flask import Flask, abort, send_from_directory, render_template
 from flask_sslify import SSLify
 from flask_seasurf import SeaSurf
 from flask_talisman import Talisman
@@ -39,7 +39,7 @@ def find_key(token):
     "frame-ancestors": "'none'",
     "object-src": "'none'",
 }
-app = Flask(__name__)
+app = Flask(__name__, template_folder=ROOT)
 app.config["SECRET_KEY"] = os.urandom(16)
 app.config["SESSION_COOKIE_NAME"] = "__Secure-session"
 app.config["SESSION_COOKIE_SAMESITE"] = "Strict"
@@ -53,6 +53,12 @@ def find_key(token):
     sslify = SSLify(app, skips=[".well-known"])
 
 
+@app.errorhandler(404)
+def page_not_found(e):
+    """Redirect to 404.html."""
+    return render_template("404.html"), 404
+
+
 @app.after_request
 def add_feature_policy(response):
     """Add feature policy."""
diff --git a/app_test.py b/app_test.py
index ea4dad2f..0861e85d 100644
--- a/app_test.py
+++ b/app_test.py
@@ -13,6 +13,7 @@
     static_proxy,
     index_redirection,
     add_feature_policy,
+    page_not_found,
 )
 
 from app import ROOT
@@ -139,6 +140,11 @@ def test_static_proxy(self):
             self.assertEqual(resp.status_code, 200)
             resp.close()
 
+    def test_page_not_found(self):
+        """Test page not found."""
+        html, status_code = page_not_found(None)
+        self.assertEqual(status_code, 404)
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/docs/404.rst b/docs/404.rst
new file mode 100644
index 00000000..57e66948
--- /dev/null
+++ b/docs/404.rst
@@ -0,0 +1,8 @@
+:orphan:
+
+404 Page Not Found
+==================
+
+What you were looking for is just not there.
+
+`Click here to go back to homepage. </>`_
diff --git a/docs/_templates/layout.html b/docs/_templates/layout.html
index 1e3acf05..5cf00693 100644
--- a/docs/_templates/layout.html
+++ b/docs/_templates/layout.html
@@ -22,5 +22,14 @@
   gtag('config', '{{ tracking_id }}');
 </script>
 {% endif -%}
+{%- if pagename == '404' -%}
+<script>
+  gtag('event', '404', {
+    'event_category': 'error',
+    'event_label': document.referrer,
+    'non_interaction': true
+  });
+</script>
+{%- endif -%}
 {% endblock %}
 {% set css_files = css_files + [ "_static/style.css" ] %}