diff --git a/pyproject.toml b/pyproject.toml
index c52c512..19cf415 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "mkdocs-include-markdown-plugin"
-version = "7.2.1"
+version = "7.2.2"
 description = "Mkdocs Markdown includer plugin."
 readme = "README.md"
 license = "Apache-2.0"
diff --git a/src/mkdocs_include_markdown_plugin/process.py b/src/mkdocs_include_markdown_plugin/process.py
index e9f2c77..f62a3b9 100644
--- a/src/mkdocs_include_markdown_plugin/process.py
+++ b/src/mkdocs_include_markdown_plugin/process.py
@@ -547,8 +547,13 @@ def key(p: str) -> str:
                 return os.path.splitext(p)[1]
     elif order_type == 'natural':
         if order_by == 'extension':
-            def key(p: str) -> str:
-                return natural_sort_key(os.path.splitext(p)[1])  # type: ignore
+            def key(p: str) -> tuple[str, str]:  # type: ignore
+                ext = os.path.splitext(p)[1].lower()
+                name = os.path.basename(p)
+                return (  # type: ignore
+                    ext,
+                    natural_sort_key(name),
+                )
         elif order_by == 'name':
             def key(p: str) -> str:
                 return natural_sort_key(os.path.basename(p))  # type: ignore