diff --git a/frontend_tests/node_tests/user_groups.js b/frontend_tests/node_tests/user_groups.js
index 6af61c33c9..4e77666eeb 100644
--- a/frontend_tests/node_tests/user_groups.js
+++ b/frontend_tests/node_tests/user_groups.js
@@ -173,18 +173,16 @@ run_test("get_recursive_subgroups", () => {
     // when determining recursive subgroups.
     // A test case that can occur in practice and would be problematic without this
     // optimization is a tree where each layer connects to every node in the next layer.
-    assert.deepEqual(user_groups.get_recursive_subgroups(admins.id), new Set([4]));
-    assert.deepEqual(user_groups.get_recursive_subgroups(all.id), new Set([4, 1, 2, 3]));
-    assert.deepEqual(user_groups.get_recursive_subgroups(test.id), new Set([2, 4, 1, 3]));
-    assert.deepEqual(user_groups.get_recursive_subgroups(foo.id), new Set([]));
-
-    blueslip.expect("error", "Could not find user group with ID 1111");
-    assert.deepEqual(user_groups.get_recursive_subgroups(1111), undefined);
+    assert.deepEqual(user_groups.get_recursive_subgroups(admins), new Set([4]));
+    assert.deepEqual(user_groups.get_recursive_subgroups(all), new Set([4, 1, 2, 3]));
+    assert.deepEqual(user_groups.get_recursive_subgroups(test), new Set([2, 4, 1, 3]));
+    assert.deepEqual(user_groups.get_recursive_subgroups(foo), new Set([]));
 
     user_groups.add_subgroups(foo.id, [9999]);
+    const foo_group = user_groups.get_user_group_from_id(foo.id);
     blueslip.expect("error", "Could not find subgroup with ID 9999", 2);
-    assert.deepEqual(user_groups.get_recursive_subgroups(foo.id), undefined);
-    assert.deepEqual(user_groups.get_recursive_subgroups(test.id), undefined);
+    assert.deepEqual(user_groups.get_recursive_subgroups(foo_group), undefined);
+    assert.deepEqual(user_groups.get_recursive_subgroups(test), undefined);
 });
 
 run_test("is_user_in_group", () => {
diff --git a/static/js/user_groups.ts b/static/js/user_groups.ts
index 048e35f1eb..0ea9f6065d 100644
--- a/static/js/user_groups.ts
+++ b/static/js/user_groups.ts
@@ -154,13 +154,7 @@ export function get_user_groups_of_user(user_id: number): UserGroup[] {
     return groups_of_user;
 }
 
-export function get_recursive_subgroups(target_group_id: number): Set<number> | undefined {
-    const target_user_group = user_group_by_id_dict.get(target_group_id);
-    if (target_user_group === undefined) {
-        blueslip.error(`Could not find user group with ID ${target_group_id}`);
-        return undefined;
-    }
-
+export function get_recursive_subgroups(target_user_group: UserGroup): Set<number> | undefined {
     // Correctness of this algorithm relying on the ES6 Set
     // implementation having the property that a `for of` loop will
     // visit all items that are added to the set during the loop.
@@ -189,7 +183,7 @@ export function is_user_in_group(user_group_id: number, user_id: number): boolea
         return true;
     }
 
-    const subgroup_ids = get_recursive_subgroups(user_group_id);
+    const subgroup_ids = get_recursive_subgroups(user_group);
     if (subgroup_ids === undefined) {
         return false;
     }