diff --git a/.changes/css-preprocessor-mime-type.md b/.changes/css-preprocessor-mime-type.md
new file mode 100644
index 000000000..9f33c38a6
--- /dev/null
+++ b/.changes/css-preprocessor-mime-type.md
@@ -0,0 +1,5 @@
+---
+"tauri-utils": patch
+---
+
+Correctly determine mime type of `.less`, `.sass` and `.styl` files.
diff --git a/core/tauri-utils/src/mime_type.rs b/core/tauri-utils/src/mime_type.rs
index 248d2a42e..d3ae5f6d9 100644
--- a/core/tauri-utils/src/mime_type.rs
+++ b/core/tauri-utils/src/mime_type.rs
@@ -49,7 +49,7 @@ impl MimeType {
     let suffix = uri.split('.').last();
     match suffix {
       Some("bin") => Self::OctetStream,
-      Some("css") => Self::Css,
+      Some("css" | "less" | "sass" | "styl") => Self::Css,
       Some("csv") => Self::Csv,
       Some("html") => Self::Html,
       Some("ico") => Self::Ico,