diff --git a/.github/workflows/tsc.yml b/.github/workflows/tsc.yml
new file mode 100644
index 0000000..112c20c
--- /dev/null
+++ b/.github/workflows/tsc.yml
@@ -0,0 +1,22 @@
+on:
+  push:
+  pull_request:
+
+jobs:
+  tsc:
+    name: tsc
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: install node v12
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+      - name: yarn install
+        run: yarn install
+      - name: tsc
+        uses: icrawl/action-tsc@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          job-name: tsc
diff --git a/src/minify.ts b/src/minify.ts
index 64927ea..7c6b881 100644
--- a/src/minify.ts
+++ b/src/minify.ts
@@ -10,6 +10,8 @@ type StateMachine = {
     }
 };
 
+let a: number = 'a'; // sample error
+
 function isSymbol(ch: string) {
     return ch == ';' || ch == ':' || ch == '{' || ch == '}' || ch == ',';
 }