diff --git a/static/js/poll_widget.js b/static/js/poll_widget.js
index 283d6cea4f..0f7b39ae70 100644
--- a/static/js/poll_widget.js
+++ b/static/js/poll_widget.js
@@ -5,6 +5,7 @@ import render_widgets_poll_widget from "../templates/widgets/poll_widget.hbs";
 import render_widgets_poll_widget_results from "../templates/widgets/poll_widget_results.hbs";
 
 import * as blueslip from "./blueslip";
+import {$t} from "./i18n";
 import * as people from "./people";
 
 export function activate({
@@ -154,11 +155,13 @@ export function activate({
 
         elem.find("button.poll-option").on("click", (e) => {
             e.stopPropagation();
+            check_option_button();
             submit_option();
         });
 
-        elem.find("input.poll-option").on("keydown", (e) => {
+        elem.find("input.poll-option").on("keyup", (e) => {
             e.stopPropagation();
+            check_option_button();
 
             if (e.key === "Enter") {
                 submit_option();
@@ -172,6 +175,23 @@ export function activate({
         });
     }
 
+    function check_option_button() {
+        const poll_option_input = elem.find("input.poll-option");
+        const option = poll_option_input.val().trim();
+        const options = poll_data.get_widget_data().options;
+
+        if (poll_data.is_option_present(options, option)) {
+            elem.find("button.poll-option").attr("disabled", true);
+            elem.find("button.poll-option").attr(
+                "title",
+                $t({defaultMessage: "Option already present."}),
+            );
+        } else {
+            elem.find("button.poll-option").attr("disabled", false);
+            elem.find("button.poll-option").removeAttr("title");
+        }
+    }
+
     function render_results() {
         const widget_data = poll_data.get_widget_data();
 
diff --git a/static/shared/js/poll_data.js b/static/shared/js/poll_data.js
index 36c4e13a48..5d9e9e9407 100644
--- a/static/shared/js/poll_data.js
+++ b/static/shared/js/poll_data.js
@@ -103,6 +103,14 @@ export class PollData {
                 // All message readers may add a new option to the poll.
                 const idx = data.idx;
                 const option = data.option;
+                const options = this.get_widget_data().options;
+
+                // While the UI doesn't allow adding duplicate options
+                // to an existing poll, the /poll command syntax to create
+                // them does not prevent duplicates, so we suppress them here.
+                if (this.is_option_present(options, option)) {
+                    return;
+                }
 
                 if (!Number.isInteger(idx) || idx < 0 || idx > MAX_IDX) {
                     this.report_error_function("poll widget: bad type for inbound option idx");