diff --git a/src/util/map.js b/src/util/map.js
index 131cf00..e3457fa 100644
--- a/src/util/map.js
+++ b/src/util/map.js
@@ -153,10 +153,11 @@ export function merge<K, V>(maps: $ReadOnlyArray<Map<K, V>>): Map<K, V> {
  * If the key is already in the map, its value will be mutated, not
  * replaced.
  */
-export function pushValue<K, V>(map: Map<K, V[]>, key: K, value: V): void {
+export function pushValue<K, V>(map: Map<K, V[]>, key: K, value: V): V[] {
   let arr = map.get(key);
   if (arr == null) {
     map.set(key, (arr = []));
   }
   arr.push(value);
+  return arr;
 }
diff --git a/src/util/map.test.js b/src/util/map.test.js
index 213f138..adbce56 100644
--- a/src/util/map.test.js
+++ b/src/util/map.test.js
@@ -325,5 +325,11 @@ describe("util/map", () => {
       MapUtil.pushValue(map, "foo", 1);
       expect(map.get("foo")).toBe(arr);
     });
+    it("returns the resultant array", () => {
+      const arr = [];
+      const map = new Map().set("foo", arr);
+      const result = MapUtil.pushValue(map, "foo", 1);
+      expect(result).toBe(arr);
+    });
   });
 });