diff --git a/README.md b/README.md
index f45ee123..db9b7eab 100644
--- a/README.md
+++ b/README.md
@@ -112,7 +112,7 @@ var result = WebIDL2.write(tree, {
      * Called only once for each types, e.g. `Document`, `Promise<DOMString>`, or `sequence<long>`.
      * @param type The `wrap()`ed result of references and syntatic bracket strings.
      */
-    type: type => type,
+    type: (type, { data }) => type,
     /**
      * Receives the return value of `reference()`. String if it's absent.
      */
diff --git a/lib/productions/argument.js b/lib/productions/argument.js
index dd6f00af..e12edee2 100644
--- a/lib/productions/argument.js
+++ b/lib/productions/argument.js
@@ -112,7 +112,7 @@ export class Argument extends Base {
     return w.ts.wrap([
       this.extAttrs.write(w),
       w.token(this.tokens.optional),
-      w.ts.type(this.idlType.write(w)),
+      w.ts.type(this.idlType.write(w), { data: this.idlType }),
       w.token(this.tokens.variadic),
       w.name_token(this.tokens.name, { data: this }),
       this.default ? this.default.write(w) : "",
diff --git a/lib/productions/attribute.js b/lib/productions/attribute.js
index 0dab2516..b20efac6 100644
--- a/lib/productions/attribute.js
+++ b/lib/productions/attribute.js
@@ -114,7 +114,7 @@ export class Attribute extends Base {
         w.token(this.tokens.special),
         w.token(this.tokens.readonly),
         w.token(this.tokens.base),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.name_token(this.tokens.name, { data: this, parent }),
         w.token(this.tokens.termination),
       ]),
diff --git a/lib/productions/callback.js b/lib/productions/callback.js
index 56dba106..24a63958 100644
--- a/lib/productions/callback.js
+++ b/lib/productions/callback.js
@@ -55,7 +55,7 @@ export class CallbackFunction extends Base {
         w.token(this.tokens.base),
         w.name_token(this.tokens.name, { data: this }),
         w.token(this.tokens.assign),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.token(this.tokens.open),
         ...this.arguments.map((arg) => arg.write(w)),
         w.token(this.tokens.close),
diff --git a/lib/productions/constant.js b/lib/productions/constant.js
index 9fd90146..4d5b6763 100644
--- a/lib/productions/constant.js
+++ b/lib/productions/constant.js
@@ -62,7 +62,7 @@ export class Constant extends Base {
       w.ts.wrap([
         this.extAttrs.write(w),
         w.token(this.tokens.base),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.name_token(this.tokens.name, { data: this, parent }),
         w.token(this.tokens.assign),
         w.token(this.tokens.value),
diff --git a/lib/productions/field.js b/lib/productions/field.js
index 1cd44ed7..40c87612 100644
--- a/lib/productions/field.js
+++ b/lib/productions/field.js
@@ -53,7 +53,7 @@ export class Field extends Base {
       w.ts.wrap([
         this.extAttrs.write(w),
         w.token(this.tokens.required),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.name_token(this.tokens.name, { data: this, parent }),
         this.default ? this.default.write(w) : "",
         w.token(this.tokens.termination),
diff --git a/lib/productions/operation.js b/lib/productions/operation.js
index f4c561be..fd6fa9cd 100644
--- a/lib/productions/operation.js
+++ b/lib/productions/operation.js
@@ -80,7 +80,7 @@ export class Operation extends Base {
     const { parent } = this;
     const body = this.idlType
       ? [
-          w.ts.type(this.idlType.write(w)),
+          w.ts.type(this.idlType.write(w), { data: this.idlType }),
           w.name_token(this.tokens.name, { data: this, parent }),
           w.token(this.tokens.open),
           w.ts.wrap(this.arguments.map((arg) => arg.write(w))),
diff --git a/lib/productions/typedef.js b/lib/productions/typedef.js
index 031898f7..d9e5b579 100644
--- a/lib/productions/typedef.js
+++ b/lib/productions/typedef.js
@@ -47,7 +47,7 @@ export class Typedef extends Base {
       w.ts.wrap([
         this.extAttrs.write(w),
         w.token(this.tokens.base),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.name_token(this.tokens.name, { data: this }),
         w.token(this.tokens.termination),
       ]),
diff --git a/test/custom-production.js b/test/custom-production.js
index d5191ff0..78699f64 100644
--- a/test/custom-production.js
+++ b/test/custom-production.js
@@ -41,7 +41,7 @@ class CustomAttribute extends Base {
       w.ts.wrap([
         this.extAttrs.write(w),
         w.token(this.tokens.base),
-        w.ts.type(this.idlType.write(w)),
+        w.ts.type(this.idlType.write(w), { data: this.idlType }),
         w.name_token(this.tokens.name, { data: this, parent }),
         w.token(this.tokens.termination),
       ]),
diff --git a/test/writer.js b/test/writer.js
index 52d04175..69222d99 100644
--- a/test/writer.js
+++ b/test/writer.js
@@ -252,4 +252,31 @@ describe("Writer template functions", () => {
       "interface[interface Misaki {interface:const[ const short MICHELLE = 1;] };]",
     );
   });
+
+  it("gives idlType object", () => {
+    const types = [];
+    rewrite(
+      `
+      interface Mizuki {
+        attribute long attr;
+        short? op(long long arg);
+      };
+      dictionary Ena {
+        sequence<unsigned short> mem;
+      };
+      `,
+      {
+        type(type, { data }) {
+          types.push(data);
+        },
+      },
+    );
+
+    expect(types[0].idlType).toBe("long");
+    expect(types[1].idlType).toBe("short");
+    expect(types[1].nullable).toBe(true);
+    expect(types[2].idlType).toBe("long long");
+    expect(types[3].generic).toBe("sequence");
+    expect(types[3].idlType[0].idlType).toBe("unsigned short");
+  });
 });