diff --git a/src/js.rs b/src/js.rs
index b35ef08a..c39d3716 100644
--- a/src/js.rs
+++ b/src/js.rs
@@ -634,6 +634,12 @@ extern {
     /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet/has
     #[wasm_bindgen(method)]
     pub fn has(this: &WeakSet, value: Object) -> bool;
+
+    /// The add() method appends a new object to the end of a WeakSet object.
+    /// 
+    /// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet/add
+    #[wasm_bindgen(method)]
+    pub fn add(this: &WeakSet, value: Object) -> WeakSet;
 }
 
 // JsString
diff --git a/tests/all/js_globals/WeakSet.rs b/tests/all/js_globals/WeakSet.rs
index 40b4be5a..2788acc3 100644
--- a/tests/all/js_globals/WeakSet.rs
+++ b/tests/all/js_globals/WeakSet.rs
@@ -58,4 +58,39 @@ fn has() {
             }
         "#)
         .test()
+}
+
+#[test]
+fn add() {
+    project()
+        .file("src/lib.rs", r#"
+            #![feature(proc_macro, wasm_custom_section)]
+
+            extern crate wasm_bindgen;
+            use wasm_bindgen::prelude::*;
+            use wasm_bindgen::js;
+
+            #[wasm_bindgen]
+            pub fn add_value(this: &js::WeakSet, value: js::Object) -> js::WeakSet {
+                this.add(value)
+            }
+        "#)
+        .file("test.ts", r#"
+            import * as assert from "assert";
+            import * as wasm from "./out";
+
+            export function test() {
+                let set = new WeakSet();
+                let value = {some: "value"};
+                wasm.add_value(set, value);
+                assert.equal(set.has(value), true);
+
+                assert.throws(() => { wasm.add_value(set, 1) }, TypeError);
+                assert.throws(() => { wasm.add_value(set, true) }, TypeError);
+                assert.throws(() => { wasm.add_value(set, "fail") }, TypeError);
+                assert.throws(() => { wasm.add_value(set, null) }, TypeError);
+                assert.throws(() => { wasm.add_value(set, undefined) }, TypeError);
+            }
+        "#)
+        .test()
 }
\ No newline at end of file