diff --git a/README.md b/README.md
index ad1e10b..221c18a 100644
--- a/README.md
+++ b/README.md
@@ -25,6 +25,16 @@ You can view the sample pages on this site.
 - [x] Dev server
 - [x] Color scheme
 
+## Constraints
+
+The filename for pages should follow the pattern below.
+
+`^[a-zA-Z0-9-.\s]+\.md$`
+
+The filename for posts should follow the pattern below.
+
+`^\d{4}-\d{2}-\d{2}-[a-zA-Z0-9-.\s]+\.md$`
+
 ## Building and running the app
 
 - Install dependencies: `npm install`
diff --git a/src/Common.fs b/src/Common.fs
index 79e08f4..62966fa 100644
--- a/src/Common.fs
+++ b/src/Common.fs
@@ -233,6 +233,12 @@ module Misc =
             | _ -> Page
         | _ -> Page
 
+    let isInvalidMarkdownFilenamePattern (s: string) =
+        Regex.IsMatch (s, @"^[a-zA-Z0-9-.\s]+\.md$") |> not
+
+    let isInvalidPostsFilenamePattern (s: string) =
+        Regex.IsMatch (s, @"^\d{4}-\d{2}-\d{2}-[a-zA-Z0-9-.\s]+\.md$") |> not
+
     type Meta =
         { frontMatter: Parser.FrontMatter option
           content: ReactElement
diff --git a/src/Generator.fs b/src/Generator.fs
index 903e055..c6807e5 100644
--- a/src/Generator.fs
+++ b/src/Generator.fs
@@ -312,9 +312,38 @@ module Rendering =
             do! IO.writeFile dest page
         }
 
+    let private checkFilenamePattern (files: string list) =
+        files
+        |> List.map IO.leaf
+        |> List.filter isInvalidMarkdownFilenamePattern
+        |> function
+           | [] -> ()
+           | x ->
+                x
+                |> String.concat " "
+                |> failwithf "Invalid filename patterns: %s"
+
+    let private checkPostsFilenamePattern (postRoot: string) (files: string list) =
+        // TODO: dirty path manipulation.
+        let postRoot = postRoot.Replace("\\", "/")
+        files
+        |> List.filter (fun s -> s.Replace("\\", "/").Contains(postRoot))
+        |> List.map IO.leaf
+        |> List.filter isInvalidPostsFilenamePattern
+        |> function
+           | [] -> ()
+           | x ->
+                x
+                |> String.concat " "
+                |> failwithf "Invalid posts filename patterns: %s"
+
     let renderMarkdowns (conf: FrameConfiguration) (site: PathConfiguration) sourceDir destDir =
         promise {
             let! files = getMarkdownFiles sourceDir
+
+            files |> checkFilenamePattern
+            files |> checkPostsFilenamePattern site.postRoot
+
             let! metas = files |> List.map readSource |> Promise.all
             let metas = metas |> Array.filter _.publish