diff --git a/web/src/compose_fade_helper.ts b/web/src/compose_fade_helper.ts
index 9b42738d65..fed984e74f 100644
--- a/web/src/compose_fade_helper.ts
+++ b/web/src/compose_fade_helper.ts
@@ -20,7 +20,7 @@ export function set_focused_recipient(recipient?: Recipient): void {
     focused_recipient = recipient;
 }
 
-export function would_receive_message(user_id: number): boolean | undefined {
+export function would_receive_message(user_id: number): boolean {
     assert(focused_recipient !== undefined);
     if (focused_recipient.type === "stream") {
         const sub = sub_store.get(focused_recipient.stream_id);
diff --git a/web/src/stream_data.ts b/web/src/stream_data.ts
index 5a03301871..0b758f8e2c 100644
--- a/web/src/stream_data.ts
+++ b/web/src/stream_data.ts
@@ -697,19 +697,19 @@ export function get_name(stream_name: string): string {
     return sub.name;
 }
 
-export function is_user_subscribed(stream_id: number, user_id: number): boolean | undefined {
+export function is_user_subscribed(stream_id: number, user_id: number): boolean {
     const sub = sub_store.get(stream_id);
     if (sub === undefined || !can_view_subscribers(sub)) {
         // 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).
+        // so we return false.
         blueslip.warn(
             "We got a is_user_subscribed call for a non-existent or inaccessible stream.",
         );
-        return undefined;
+        return false;
     }
     if (user_id === undefined) {
         blueslip.warn("Undefined user_id passed to function is_user_subscribed");
-        return undefined;
+        return false;
     }
 
     return peer_data.is_user_subscribed(stream_id, user_id);
diff --git a/web/tests/peer_data.test.js b/web/tests/peer_data.test.js
index 169a9fa6bc..c0248175e8 100644
--- a/web/tests/peer_data.test.js
+++ b/web/tests/peer_data.test.js
@@ -152,7 +152,7 @@ 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(stream_id, undefined), undefined);
+    assert.ok(!stream_data.is_user_subscribed(stream_id, undefined));
     blueslip.reset();
 
     // Verify noop for bad stream when removing subscriber
@@ -193,9 +193,9 @@ test("subscribers", () => {
         2,
     );
     sub.invite_only = true;
-    assert.equal(stream_data.is_user_subscribed(stream_id, brutus.user_id), undefined);
+    assert.ok(!stream_data.is_user_subscribed(stream_id, brutus.user_id));
     peer_data.remove_subscriber(stream_id, brutus.user_id);
-    assert.equal(stream_data.is_user_subscribed(stream_id, brutus.user_id), undefined);
+    assert.ok(!stream_data.is_user_subscribed(stream_id, brutus.user_id));
     blueslip.reset();
 
     // Verify that we don't crash for a bad stream.