diff --git a/src/upgrades/4.3.0/fix_duplicate_handles.js b/src/upgrades/4.3.0/fix_duplicate_handles.js
new file mode 100644
index 0000000000..d3c62f712f
--- /dev/null
+++ b/src/upgrades/4.3.0/fix_duplicate_handles.js
@@ -0,0 +1,89 @@
+'use strict';
+
+const user = require('../../user');
+const categories = require('../../categories');
+const activitypub = require('../../activitypub');
+
+const db = require('../../database');
+
+module.exports = {
+	// you should use spaces
+	// the underscores are there so you can double click to select the whole thing
+	name: 'Fix duplicate accounts sharing identical handles',
+	// remember, month is zero-indexed (so January is 0, December is 11)
+	timestamp: Date.UTC(2025, 3, 29),
+	method: async function () {
+		const { progress } = this;
+
+		// Build list of duplicate remote user handles
+		let handles = await db.getSortedSetMembers('ap.preferredUsername:sorted');
+		handles = handles.map(handle => handle.split(':https://')[0]);
+		const duplicateUsers = new Set();
+		handles.forEach((handle, idx) => {
+			if (handles.indexOf(handle) !== idx) {
+				duplicateUsers.add(handle);
+			}
+		});
+
+		// Build list of duplicate remote category handles
+		handles = await db.getSortedSetMembers('categories:name');
+		handles = handles
+			.filter(handle => handle.indexOf('@') !== -1) // zset contains category names too
+			.map(handle => handle.split(':https://')[0]);
+		const duplicateCategories = new Set();
+		handles.forEach((handle, idx) => {
+			if (handles.indexOf(handle) !== idx) {
+				duplicateCategories.add(handle);
+			}
+		});
+
+		progress.total = duplicateUsers.size + duplicateCategories.size;
+
+		// Find real user, fix handle reference, delete the rest
+		await Promise.all(Array.from(duplicateUsers).map(async (handle) => {
+			const max = '(' + handle.substr(0, handle.length - 1) + String.fromCharCode(handle.charCodeAt(handle.length - 1) + 1);
+			let ids = await db.getSortedSetRangeByLex('ap.preferredUsername:sorted', `[${handle}`, max);
+			ids = ids.map(id => id.slice(handle.length + 1));
+			const { actorUri: canonicalId } = await activitypub.helpers.query(handle);
+
+			await Promise.all(ids.map(async (id) => {
+				if (id !== canonicalId) {
+					try {
+						await user.deleteAccount(id);
+					} catch (e) {
+						// User doesn't exist, maybe never did.
+						await db.sortedSetRemove('ap.preferredUsername:sorted', `${handle}:${id}`);
+					}
+				}
+			}));
+
+			// Fix handle:uid backreference or delete
+			if (canonicalId) {
+				await db.setObjectField('handle:uid', handle, canonicalId);
+			}
+
+			progress.incr();
+		}));
+
+		// Find real category, fix handle reference, delete the rest
+		await Promise.all(Array.from(duplicateCategories).map(async (handle) => {
+			const max = '(' + handle.substr(0, handle.length - 1) + String.fromCharCode(handle.charCodeAt(handle.length - 1) + 1);
+			let ids = await db.getSortedSetRangeByLex('categories:name', `[${handle}`, max);
+			ids = ids.map(id => id.slice(handle.length + 1));
+			const { actorUri: canonicalId } = await activitypub.helpers.query(handle);
+
+			await Promise.all(ids.map(async (id) => {
+				if (id !== canonicalId) {
+					await categories.purge(id, 0);
+				}
+			}));
+
+			// Fix handle:uid backreference or delete
+			if (canonicalId) {
+				await db.setObjectField('handle:cid', handle, canonicalId);
+			}
+
+			progress.incr();
+		}));
+	},
+};