diff --git a/web/src/compose_actions.js b/web/src/compose_actions.js
index 333b514d88..526a666ee3 100644
--- a/web/src/compose_actions.js
+++ b/web/src/compose_actions.js
@@ -332,7 +332,7 @@ export function cancel() {
     clear_box();
     compose_banner.clear_message_sent_banners();
     call_hooks(compose_cancel_hooks);
-    compose_state.set_message_type(false);
+    compose_state.set_message_type(undefined);
     compose_pm_pill.clear();
     $(document).trigger("compose_canceled.zulip");
 }
diff --git a/web/src/compose_state.ts b/web/src/compose_state.ts
index abfea4f0fa..ef0d433051 100644
--- a/web/src/compose_state.ts
+++ b/web/src/compose_state.ts
@@ -5,9 +5,9 @@ import {$t} from "./i18n";
 import * as people from "./people";
 import * as sub_store from "./sub_store";
 
-let message_type: "stream" | "private" | false = false;
+let message_type: "stream" | "private" | undefined;
 let recipient_edited_manually = false;
-let last_focused_compose_type_input: HTMLInputElement | false = false; // an HTML input element or false-y
+let last_focused_compose_type_input: HTMLInputElement | undefined;
 
 // We use this variable to keep track of whether user has viewed the topic resolved
 // banner for the current compose session, for a narrow. This prevents the banner
@@ -29,15 +29,15 @@ export function set_last_focused_compose_type_input(element: HTMLInputElement):
     last_focused_compose_type_input = element;
 }
 
-export function get_last_focused_compose_type_input(): HTMLInputElement | false {
+export function get_last_focused_compose_type_input(): HTMLInputElement | undefined {
     return last_focused_compose_type_input;
 }
 
-export function set_message_type(msg_type: "stream" | "private" | false): void {
+export function set_message_type(msg_type: "stream" | "private" | undefined): void {
     message_type = msg_type;
 }
 
-export function get_message_type(): "stream" | "private" | false {
+export function get_message_type(): "stream" | "private" | undefined {
     return message_type;
 }
 
diff --git a/web/tests/compose.test.js b/web/tests/compose.test.js
index 743a52e586..be61661f60 100644
--- a/web/tests/compose.test.js
+++ b/web/tests/compose.test.js
@@ -564,7 +564,7 @@ test_ui("update_fade", ({override, override_rewire}) => {
         update_narrow_to_recipient_visibility_called = true;
     });
 
-    compose_state.set_message_type(false);
+    compose_state.set_message_type(undefined);
     compose_recipient.update_on_recipient_change();
     assert.ok(!set_focused_recipient_checked);
     assert.ok(!update_all_called);
diff --git a/web/tests/compose_actions.test.js b/web/tests/compose_actions.test.js
index 9cc5baa5ec..8ad03ff367 100644
--- a/web/tests/compose_actions.test.js
+++ b/web/tests/compose_actions.test.js
@@ -100,14 +100,14 @@ function test(label, f) {
         $(".new_message_textarea").css = noop;
 
         people.init();
-        compose_state.set_message_type(false);
+        compose_state.set_message_type(undefined);
         f(helpers);
     });
 }
 
 test("initial_state", () => {
     assert.equal(compose_state.composing(), false);
-    assert.equal(compose_state.get_message_type(), false);
+    assert.equal(compose_state.get_message_type(), undefined);
     assert.equal(compose_state.has_message_content(), false);
 });
 
@@ -466,7 +466,7 @@ test("focus_in_empty_compose", () => {
     $("textarea#compose-textarea").val("");
     assert.ok(compose_state.focus_in_empty_compose());
 
-    compose_state.set_message_type(false);
+    compose_state.set_message_type(undefined);
     assert.ok(!compose_state.focus_in_empty_compose());
 
     $("textarea#compose-textarea").val("foo");
diff --git a/web/tests/drafts.test.js b/web/tests/drafts.test.js
index a795033348..3d1d7c5148 100644
--- a/web/tests/drafts.test.js
+++ b/web/tests/drafts.test.js
@@ -244,7 +244,7 @@ test("remove_old_drafts", () => {
 });
 
 test("update_draft", ({override, override_rewire}) => {
-    compose_state.set_message_type(false);
+    compose_state.set_message_type(undefined);
     let draft_id = drafts.update_draft();
     assert.equal(draft_id, undefined);
 
diff --git a/web/tests/narrow.test.js b/web/tests/narrow.test.js
index 2f96d80da9..2859d6f631 100644
--- a/web/tests/narrow.test.js
+++ b/web/tests/narrow.test.js
@@ -660,7 +660,7 @@ run_test("narrow_to_compose_target errors", ({disallow_rewire}) => {
     disallow_rewire(narrow, "activate");
 
     // No-op when not composing.
-    compose_state.set_message_type(false);
+    compose_state.set_message_type(undefined);
     narrow.to_compose_target();
 
     // No-op when empty stream.