diff --git a/frontend_tests/node_tests/compose.js b/frontend_tests/node_tests/compose.js
index a3bb7fb1ff..1afa0da7a7 100644
--- a/frontend_tests/node_tests/compose.js
+++ b/frontend_tests/node_tests/compose.js
@@ -1138,9 +1138,10 @@ run_test('warn_if_mentioning_unsubscribed_user', () => {
     const checks = [
         (function () {
             let called;
-            compose.needs_subscribe_warning = function (user_id) {
+            compose.needs_subscribe_warning = function (user_id, stream_id) {
                 called = true;
                 assert.equal(user_id, 34);
+                assert.equal(stream_id, 111);
                 return true;
             };
             return function () { assert(called); };
diff --git a/frontend_tests/node_tests/stream_data.js b/frontend_tests/node_tests/stream_data.js
index a34f634f82..868631584c 100644
--- a/frontend_tests/node_tests/stream_data.js
+++ b/frontend_tests/node_tests/stream_data.js
@@ -206,10 +206,10 @@ run_test('subscribers', () => {
 
     stream_data.set_subscribers(sub, [me.user_id, fred.user_id, george.user_id]);
     stream_data.update_calculated_fields(sub);
-    assert(stream_data.is_user_subscribed('Rome', me.user_id));
-    assert(stream_data.is_user_subscribed('Rome', fred.user_id));
-    assert(stream_data.is_user_subscribed('Rome', george.user_id));
-    assert(!stream_data.is_user_subscribed('Rome', not_fred.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, me.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, fred.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, george.user_id));
+    assert(!stream_data.is_user_subscribed(sub.stream_id, not_fred.user_id));
 
     assert.deepEqual(
         potential_subscriber_ids(),
@@ -226,12 +226,12 @@ run_test('subscribers', () => {
         user_id: 104,
     };
     people.add_active_user(brutus);
-    assert(!stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(!stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
 
     // add
     let ok = stream_data.add_subscriber(sub.stream_id, brutus.user_id);
     assert(ok);
-    assert(stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
     sub = stream_data.get_sub('Rome');
     stream_data.update_subscribers_count(sub);
     assert.equal(sub.subscriber_count, 1);
@@ -241,7 +241,7 @@ run_test('subscribers', () => {
 
     // verify that adding an already-added subscriber is a noop
     stream_data.add_subscriber(sub.stream_id, brutus.user_id);
-    assert(stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
     sub = stream_data.get_sub('Rome');
     stream_data.update_subscribers_count(sub);
     assert.equal(sub.subscriber_count, 1);
@@ -249,7 +249,7 @@ run_test('subscribers', () => {
     // remove
     ok = stream_data.remove_subscriber(sub.stream_id, brutus.user_id);
     assert(ok);
-    assert(!stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(!stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
     sub = stream_data.get_sub('Rome');
     stream_data.update_subscribers_count(sub);
     assert.equal(sub.subscriber_count, 0);
@@ -257,7 +257,7 @@ run_test('subscribers', () => {
     // verify that checking subscription with undefined user id
 
     blueslip.expect('warn', 'Undefined user_id passed to function is_user_subscribed');
-    assert.equal(stream_data.is_user_subscribed('Rome', undefined), undefined);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, undefined), undefined);
 
     // Verify noop for bad stream when removing subscriber
     const bad_stream_id = 999999;
@@ -269,7 +269,7 @@ run_test('subscribers', () => {
     blueslip.expect('warn', 'We tried to remove invalid subscriber: 104');
     ok = stream_data.remove_subscriber(sub.stream_id, brutus.user_id);
     assert(!ok);
-    assert(!stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(!stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
     sub = stream_data.get_sub('Rome');
     stream_data.update_subscribers_count(sub);
     assert.equal(sub.subscriber_count, 0);
@@ -280,27 +280,27 @@ run_test('subscribers', () => {
     stream_data.add_sub(sub);
     stream_data.add_subscriber(sub.stream_id, brutus.user_id);
     sub.subscribed = true;
-    assert(stream_data.is_user_subscribed('Rome', brutus.user_id));
+    assert(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id));
 
     // Verify that we noop and don't crash when unsubscribed.
     sub.subscribed = false;
     stream_data.update_calculated_fields(sub);
     ok = stream_data.add_subscriber(sub.stream_id, brutus.user_id);
     assert(ok);
-    assert.equal(stream_data.is_user_subscribed('Rome', brutus.user_id), true);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id), true);
     stream_data.remove_subscriber(sub.stream_id, brutus.user_id);
-    assert.equal(stream_data.is_user_subscribed('Rome', brutus.user_id), false);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id), false);
     stream_data.add_subscriber(sub.stream_id, brutus.user_id);
-    assert.equal(stream_data.is_user_subscribed('Rome', brutus.user_id), true);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id), true);
 
     blueslip.expect(
         'warn',
         'We got a is_user_subscribed call for a non-existent or inaccessible stream.', 2);
     sub.invite_only = true;
     stream_data.update_calculated_fields(sub);
-    assert.equal(stream_data.is_user_subscribed('Rome', brutus.user_id), undefined);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id), undefined);
     stream_data.remove_subscriber(sub.stream_id, brutus.user_id);
-    assert.equal(stream_data.is_user_subscribed('Rome', brutus.user_id), undefined);
+    assert.equal(stream_data.is_user_subscribed(sub.stream_id, brutus.user_id), undefined);
 
     // Verify that we don't crash and return false for a bad stream.
     blueslip.expect(
diff --git a/static/js/compose.js b/static/js/compose.js
index 7625434114..ded95388bf 100644
--- a/static/js/compose.js
+++ b/static/js/compose.js
@@ -746,7 +746,7 @@ exports.handle_keyup = function (event, textarea) {
     rtl.set_rtl_class_for_textarea(textarea);
 };
 
-exports.needs_subscribe_warning = function (user_id, stream_name) {
+exports.needs_subscribe_warning = function (user_id, stream_id) {
     // This returns true if all of these conditions are met:
     //  * the user is valid
     //  * the user is not already subscribed to the stream
@@ -772,7 +772,7 @@ exports.needs_subscribe_warning = function (user_id, stream_name) {
         return false;
     }
 
-    if (stream_data.is_user_subscribed(stream_name, user_id)) {
+    if (stream_data.is_user_subscribed(stream_id, user_id)) {
         // If our user is already subscribed
         return false;
     }
@@ -917,7 +917,7 @@ exports.warn_if_mentioning_unsubscribed_user = function (mentioned) {
         return;
     }
 
-    if (exports.needs_subscribe_warning(user_id, sub.name)) {
+    if (exports.needs_subscribe_warning(user_id, sub.stream_id)) {
         const error_area = $("#compose_invite_users");
         const existing_invites_area = $('#compose_invite_users .compose_invite_user');
 
diff --git a/static/js/compose_fade.js b/static/js/compose_fade.js
index 41b8338bce..9d833b08d3 100644
--- a/static/js/compose_fade.js
+++ b/static/js/compose_fade.js
@@ -102,7 +102,7 @@ exports.would_receive_message = function (user_id) {
             return true;
         }
 
-        return stream_data.is_user_subscribed(focused_recipient.stream, user_id);
+        return stream_data.is_user_subscribed(focused_recipient.stream_id, user_id);
     }
 
     // PM, so check if the given email is in the recipients list.
diff --git a/static/js/stream_data.js b/static/js/stream_data.js
index 84a92af2f8..8c53dca864 100644
--- a/static/js/stream_data.js
+++ b/static/js/stream_data.js
@@ -683,8 +683,8 @@ exports.remove_subscriber = function (stream_id, user_id) {
     return true;
 };
 
-exports.is_user_subscribed = function (stream_name, user_id) {
-    const sub = exports.get_sub(stream_name);
+exports.is_user_subscribed = function (stream_id, user_id) {
+    const sub = exports.get_sub_by_id(stream_id);
     if (typeof sub === 'undefined' || !sub.can_access_subscribers) {
         // If we don't know about the stream, or we ourselves cannot access subscriber list,
         // so we return undefined (treated as falsy if not explicitly handled).
diff --git a/static/js/stream_events.js b/static/js/stream_events.js
index 688ded30c5..07b5735d45 100644
--- a/static/js/stream_events.js
+++ b/static/js/stream_events.js
@@ -136,7 +136,7 @@ exports.remove_deactivated_user_from_all_streams = function (user_id) {
     const all_subs = stream_data.get_unsorted_subs();
 
     for (const sub of all_subs) {
-        if (stream_data.is_user_subscribed(sub.name, user_id)) {
+        if (stream_data.is_user_subscribed(sub.stream_id, user_id)) {
             stream_data.remove_subscriber(sub.stream_id, user_id);
             subs.rerender_subscriptions_settings(sub);
         }
diff --git a/static/js/typeahead_helper.js b/static/js/typeahead_helper.js
index 4015b01d33..53fb31a139 100644
--- a/static/js/typeahead_helper.js
+++ b/static/js/typeahead_helper.js
@@ -191,7 +191,7 @@ exports.compare_people_for_relevance = function (
     person_a,
     person_b,
     tertiary_compare,
-    current_stream) {
+    current_stream_id) {
 
     // give preference to "all", "everyone" or "stream"
     // We use is_broadcast for a quick check.  It will
@@ -209,9 +209,9 @@ exports.compare_people_for_relevance = function (
     // Now handle actual people users.
 
     // give preference to subscribed users first
-    if (current_stream !== undefined) {
-        const a_is_sub = stream_data.is_user_subscribed(current_stream, person_a.user_id);
-        const b_is_sub = stream_data.is_user_subscribed(current_stream, person_b.user_id);
+    if (current_stream_id !== undefined) {
+        const a_is_sub = stream_data.is_user_subscribed(current_stream_id, person_a.user_id);
+        const b_is_sub = stream_data.is_user_subscribed(current_stream_id, person_b.user_id);
 
         if (a_is_sub && !b_is_sub) {
             return -1;
@@ -257,7 +257,7 @@ exports.sort_people_for_relevance = function (objs, current_stream_name, current
                 stream_id,
                 current_topic,
             ),
-            current_stream.name,
+            current_stream.stream_id,
         ));
     }