diff --git a/internal/web/files.go b/internal/web/files.go
index 07b91a7..91b35b8 100644
--- a/internal/web/files.go
+++ b/internal/web/files.go
@@ -142,7 +142,7 @@ func (s *Server) handleFilesMkdir(w http.ResponseWriter, r *http.Request, root,
 	}
 	name := strings.TrimSpace(r.PostForm.Get("name"))
 	if !resourceNameRe.MatchString(name) {
-		http.Error(w, "name must be 1-64 letters, digits, '-' or '_'", http.StatusBadRequest)
+		http.Error(w, "name must be 1-64 letters, digits, dots, '-' or '_'", http.StatusBadRequest)
 		return
 	}
 
diff --git a/internal/web/resources.go b/internal/web/resources.go
index 6e051a4..8d76f19 100644
--- a/internal/web/resources.go
+++ b/internal/web/resources.go
@@ -12,7 +12,8 @@ import (
 
 // resourceNameRe restricts calendar/address book names to characters that
 // are safe as both a URL path segment and a filesystem directory name.
-var resourceNameRe = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,64}$`)
+// Includes dots for hidden files/folders (Unix convention).
+var resourceNameRe = regexp.MustCompile(`^[a-zA-Z0-9._-]{1,64}$`)
 
 // hexColorRe validates the 6-digit hex color format produced by an HTML
 // <input type="color">, e.g. "#3b82f6".
diff --git a/web/static/files.js b/web/static/files.js
index 47a779b..5bdcbc6 100644
--- a/web/static/files.js
+++ b/web/static/files.js
@@ -56,7 +56,7 @@
         void upload(Array.from(folderInput.files || []));
         folderInput.value = "";
     });
-    const folderNameRe = /^[a-zA-Z0-9_-]{1,64}$/;
+    const folderNameRe = /^[a-zA-Z0-9._-]{1,64}$/;
     newFolderButton?.addEventListener("click", async () => {
         const name = window.prompt("New folder name:");
         if (!name) {
diff --git a/web/ts/files.ts b/web/ts/files.ts
index dd98de0..6c1742d 100644
--- a/web/ts/files.ts
+++ b/web/ts/files.ts
@@ -61,7 +61,7 @@
 		folderInput.value = "";
 	});
 
-	const folderNameRe = /^[a-zA-Z0-9_-]{1,64}$/;
+	const folderNameRe = /^[a-zA-Z0-9._-]{1,64}$/;
 
 	newFolderButton?.addEventListener("click", async () => {
 		const name = window.prompt("New folder name:");