diff --git a/frontend_tests/node_tests/compose.js b/frontend_tests/node_tests/compose.js
index 1b44c3f435..9efe078088 100644
--- a/frontend_tests/node_tests/compose.js
+++ b/frontend_tests/node_tests/compose.js
@@ -43,6 +43,7 @@ const server_events = mock_esm("../../static/js/server_events");
 const transmit = mock_esm("../../static/js/transmit");
 const upload = mock_esm("../../static/js/upload");
 
+const compose_ui = zrequire("compose_ui");
 const compose_closed_ui = zrequire("compose_closed_ui");
 const compose_state = zrequire("compose_state");
 const compose = zrequire("compose");
@@ -361,6 +362,7 @@ test_ui("finish", ({override, override_rewire, mock_template}) => {
         $("#compose-send-button .loader").hide();
         $("#compose-textarea").off("select");
         $("#compose-textarea").val("");
+        compose_ui.compose_spinner_visible = false;
         const res = compose.finish();
         assert.equal(res, false);
         assert.ok(!$("#compose_banners .recipient_not_subscribed").visible());
@@ -374,6 +376,7 @@ test_ui("finish", ({override, override_rewire, mock_template}) => {
         $("#compose .preview_message_area").show();
         $("#compose .markdown_preview").hide();
         $("#compose-textarea").val("foobarfoobar");
+        compose_ui.compose_spinner_visible = false;
         compose_state.set_message_type("private");
         override(compose_pm_pill, "get_emails", () => "bob@example.com");
         override(compose_pm_pill, "get_user_ids", () => []);
@@ -399,6 +402,7 @@ test_ui("finish", ({override, override_rewire, mock_template}) => {
         $("#compose .preview_message_area").show();
         $("#compose .markdown_preview").hide();
         $("#compose-textarea").val("foobarfoobar");
+        compose_ui.compose_spinner_visible = false;
         compose_state.set_message_type("stream");
         compose_state.set_stream_name("social");
         override_rewire(people, "get_by_user_id", () => []);
diff --git a/static/js/compose.js b/static/js/compose.js
index 13fd1f4def..e61e597ea3 100644
--- a/static/js/compose.js
+++ b/static/js/compose.js
@@ -290,7 +290,17 @@ export function enter_with_preview_open(ctrl_pressed = false) {
     }
 }
 
+// Common entrypoint for asking the server to send the message
+// currently drafted in the compose box, including for scheduled
+// messages.
 export function finish() {
+    if (compose_ui.compose_spinner_visible) {
+        // Avoid sending a message twice in parallel in races where
+        // the user clicks the `Send` button very quickly twice or
+        // presses enter and the send button simultaneously.
+        return undefined;
+    }
+
     clear_preview_area();
     clear_invites();
     clear_private_stream_alert();
diff --git a/static/js/compose_ui.js b/static/js/compose_ui.js
index 22661ab314..8e7ca68cb5 100644
--- a/static/js/compose_ui.js
+++ b/static/js/compose_ui.js
@@ -10,6 +10,7 @@ import * as popover_menus from "./popover_menus";
 import * as rtl from "./rtl";
 import * as user_status from "./user_status";
 
+export let compose_spinner_visible = false;
 let full_size_status = false; // true or false
 
 // Some functions to handle the full size status explicitly
@@ -404,12 +405,14 @@ export function format_text($textarea, type) {
 }
 
 export function hide_compose_spinner() {
+    compose_spinner_visible = false;
     $("#compose-send-button .loader").hide();
     $("#compose-send-button span").show();
     $("#compose-send-button").removeClass("disable-btn");
 }
 
 export function show_compose_spinner() {
+    compose_spinner_visible = true;
     // Always use white spinner.
     loading.show_button_spinner($("#compose-send-button .loader"), true);
     $("#compose-send-button span").hide();