diff --git a/hbjs.cc b/hbjs.cc
index 946ab2d..849a43b 100644
--- a/hbjs.cc
+++ b/hbjs.cc
@@ -190,6 +190,11 @@ static hb_bool_t do_trace (hb_buffer_t *buffer,
     HB_BUFFER_SERIALIZE_FORMAT_JSON,
     HB_BUFFER_SERIALIZE_FLAG_NO_GLYPH_NAMES);
   user_data->consumed += consumed;
+  if (hb_buffer_get_content_type(buffer) == HB_BUFFER_CONTENT_TYPE_GLYPHS) {
+    _user_data_printf (user_data, ", \"glyphs\": true");
+  } else {
+    _user_data_printf (user_data, ", \"glyphs\": false");
+  }
   _user_data_printf (user_data, "},\n");
 
   return 1;
diff --git a/test/index.js b/test/index.js
index d7b9ae0..f7a69cd 100644
--- a/test/index.js
+++ b/test/index.js
@@ -153,4 +153,33 @@ describe('shape', function () {
     expect(glyphs[2]).to.deep.equal({cl: 1, g: 101, ax: 269, ay: 0, dx: 0, dy: 0, flags: 0} /* ب */);
     expect(glyphs[3]).to.deep.equal({cl: 0, g:  50, ax: 235, ay: 0, dx: 0, dy: 0, flags: 0} /* أ */);
   });
+
+  it('shape with tracing', function () {
+    this.blob = hb.createBlob(fs.readFileSync(path.join(__dirname, 'fonts/noto/NotoSans-Regular.ttf')));
+    this.face = hb.createFace(this.blob);
+    this.font = hb.createFont(this.face);
+    this.buffer = hb.createBuffer();
+    this.buffer.addText('abc');
+    this.buffer.guessSegmentProperties();
+    const result = hb.shapeWithTrace(this.font, this.buffer, 0, 0)
+    expect(result).to.have.lengthOf(42);
+    expect(result[0]).to.deep.equal({
+      "m": "start table GSUB",
+      "glyphs": true,
+      "t": [
+        {cl: 0, g: 68},
+        {cl: 1, g: 69},
+        {cl: 2, g: 70},
+      ],
+    });
+    expect(result[41]).to.deep.equal({
+      "m": "end table GPOS",
+      "glyphs": true,
+      "t": [
+        {cl: 0, g: 68, ax: 561, ay: 0, dx: 0, dy: 0},
+        {cl: 1, g: 69, ax: 615, ay: 0, dx: 0, dy: 0},
+        {cl: 2, g: 70, ax: 480, ay: 0, dx: 0, dy: 0},
+      ],
+    });
+  });
 });