diff --git a/js-tests/index.js b/js-tests/index.js
index 14cdb69..7e535f5 100644
--- a/js-tests/index.js
+++ b/js-tests/index.js
@@ -38,9 +38,10 @@ test("biscuit builder", function(t) {
   builder.addFact(fact`fact(${userId})`);
   builder.addRule(rule`u($id) <- user($id, ${userId})`);
   builder.addCheck(check`check if check(${userId})`);
+  builder.setRootKeyId(1234);
   t.equal(
     builder.toString(),
-    `// no root key id set
+    `// root key id: 1234
 user("1234");
 fact("1234");
 u($id) <- user($id, "1234");
diff --git a/src/builder.rs b/src/builder.rs
index 6f08264..15e8a72 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -36,6 +36,12 @@ impl BiscuitBuilder {
         self.0.merge(other.0.clone())
     }
 
+    /// Sets the root key id
+    #[wasm_bindgen(js_name = setRootKeyId)]
+    pub fn set_root_key_id(&mut self, root_key_id: u32) {
+        self.0.set_root_key_id(root_key_id)
+    }
+
     /// Adds a Datalog fact
     #[wasm_bindgen(js_name = addFact)]
     pub fn add_fact(&mut self, fact: &Fact) -> Result<(), JsValue> {