diff --git a/package.json b/package.json
index 4b8a488..a81494f 100644
--- a/package.json
+++ b/package.json
@@ -18,6 +18,7 @@
     "vscode": "^1.68.0"
   },
   "activationEvents": [
+    "onLanguage:haml",
     "onLanguage:ruby",
     "workspaceContains:Gemfile.lock",
     "onCommand:syntaxTree.start",
diff --git a/src/extension.ts b/src/extension.ts
index 0f7b3c6..a326cbf 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -134,6 +134,7 @@ export async function activate(context: ExtensionContext) {
     // responsible for the communication and management of the Ruby subprocess.
     languageClient = new LanguageClient("Syntax Tree", { run, debug: run }, {
       documentSelector: [
+        { scheme: "file", language: "haml" },
         { scheme: "file", language: "ruby" },
       ],
       outputChannel