diff --git a/lib/cmd/cov.js b/lib/cmd/cov.js
index 45410a02..b6c4404d 100644
--- a/lib/cmd/cov.js
+++ b/lib/cmd/cov.js
@@ -104,13 +104,11 @@ class CovCommand extends Command {
       '-r', 'json-summary',
       '-r', 'json',
       '-r', 'lcov',
-      '--extension', '.ts',
     ];
 
     // typescript support
-    if (context.typescript) {
-      covArgs.push('--extension');
-      covArgs.push('.ts');
+    if (context.argv.typescript) {
+      covArgs.push('--extension', '.ts');
       this.addExclude('typings/');
       this.addExclude('**/*.d.ts');
     }
diff --git a/test/fixtures/example-ts/package.json b/test/fixtures/example-ts/package.json
index 1ab2c3f9..24d8c3e5 100644
--- a/test/fixtures/example-ts/package.json
+++ b/test/fixtures/example-ts/package.json
@@ -1,3 +1,6 @@
 {
-  "name": "example-ts"
+  "name": "example-ts",
+  "egg": {
+    "typescript": true
+  }
 }
\ No newline at end of file
diff --git a/test/ts.test.js b/test/ts.test.js
index cf77db6e..05d0e741 100644
--- a/test/ts.test.js
+++ b/test/ts.test.js
@@ -63,7 +63,7 @@ describe('test/ts.test.js', () => {
 
     it('should cov app', () => {
       return coffee.fork(eggBin, [ 'cov', '--ts' ], { cwd })
-        .debug()
+        // .debug()
         .expect('stdout', /hi, egg, 123456/)
         .expect('stdout', process.env.NYC_ROOT_ID ? /Coverage summary/ : /Statements.*100%/)
         .expect('code', 0)