diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2310ef9376..962c32366a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ### Fixed
 - [#2114](https://github.com/plotly/dash/pull/2114) Fix bug [#1978](https://github.com/plotly/dash/issues/1978) where text could not be copied from cells in tables with `cell_selectable=False`.
 - [#2102](https://github.com/plotly/dash/pull/2102) Fix bug as reported in [dash-labs #113](https://github.com/plotly/dash-labs/issues/113) where files starting with `.` were not excluded when building `dash.page_registry`.
+- [#2100](https://github.com/plotly/dash/pull/2100) Fixes bug where module name in for a custom `not_found_404` page is incorrect in the `dash.page_registry` when not using the `pages` folder.
 - [#2098](https://github.com/plotly/dash/pull/2098) Accept HTTP code 400 as well as 401 for JWT expiry
 - [#2097](https://github.com/plotly/dash/pull/2097) Fix bug [#2095](https://github.com/plotly/dash/issues/2095) with TypeScript compiler and `React.FC` empty valueDeclaration error & support empty props components.
 - [#2104](https://github.com/plotly/dash/pull/2104) Fix bug [#2099](https://github.com/plotly/dash/issues/2099) with Dropdown clearing search value when a value is selected.
diff --git a/dash/dash.py b/dash/dash.py
index 782c38611d..e91fbce46a 100644
--- a/dash/dash.py
+++ b/dash/dash.py
@@ -2044,7 +2044,11 @@ def update(pathname, search):
 
                 # get layout
                 if page == {}:
-                    module_404 = ".".join([self.pages_folder, "not_found_404"])
+                    module_404 = (
+                        ".".join([self.pages_folder, "not_found_404"])
+                        if self.pages_folder
+                        else "not_found_404"
+                    )
                     not_found_404 = _pages.PAGE_REGISTRY.get(module_404)
                     if not_found_404:
                         layout = not_found_404["layout"]
diff --git a/tests/integration/test_integration.py b/tests/integration/test_integration.py
index d2659ac54f..ab88a45b8f 100644
--- a/tests/integration/test_integration.py
+++ b/tests/integration/test_integration.py
@@ -389,6 +389,12 @@ def test_inin027_multi_page_without_pages_folder(dash_duo):
         id="multi_layout2",
     )
 
+    dash.register_page(
+        "not_found_404",
+        layout=html.Div("text for not_found_404", id="text_not_found_404"),
+        id="not_found_404",
+    )
+
     app.layout = html.Div(
         [
             html.Div(
@@ -414,4 +420,10 @@ def test_inin027_multi_page_without_pages_folder(dash_duo):
         dash_duo.wait_for_text_to_equal("#text_" + page["id"], "text for " + page["id"])
         assert dash_duo.driver.title == page["title"], "check that page title updates"
 
+    # test registration of not_found_404
+    assert "not_found_404" in dash.page_registry.keys(), "check custom not_found_404"
+
+    # clean up so this page doesn't affect other tests
+    del dash.page_registry["not_found_404"]
+
     assert not dash_duo.get_logs()