diff --git a/src/editor/deserialize.js b/src/editor/deserialize.ts
similarity index 84%
rename from src/editor/deserialize.js
rename to src/editor/deserialize.ts
index 190963f357..48d1d98ae4 100644
--- a/src/editor/deserialize.js
+++ b/src/editor/deserialize.ts
@@ -1,6 +1,6 @@
 /*
 Copyright 2019 New Vector Ltd
-Copyright 2019 The Matrix.org Foundation C.I.C.
+Copyright 2019, 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -15,11 +15,14 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { MatrixEvent } from "matrix-js-sdk/src/models/event";
+
 import { walkDOMDepthFirst } from "./dom";
 import { checkBlockNode } from "../HtmlUtils";
-import {getPrimaryPermalinkEntity} from "../utils/permalinks/Permalinks";
+import { getPrimaryPermalinkEntity } from "../utils/permalinks/Permalinks";
+import { PartCreator } from "./parts";
 
-function parseAtRoomMentions(text, partCreator) {
+function parseAtRoomMentions(text: string, partCreator: PartCreator) {
     const ATROOM = "@room";
     const parts = [];
     text.split(ATROOM).forEach((textPart, i, arr) => {
@@ -37,7 +40,7 @@ function parseAtRoomMentions(text, partCreator) {
     return parts;
 }
 
-function parseLink(a, partCreator) {
+function parseLink(a: HTMLAnchorElement, partCreator: PartCreator) {
     const {href} = a;
     const resourceId = getPrimaryPermalinkEntity(href); // The room/user ID
     const prefix = resourceId ? resourceId[0] : undefined; // First character of ID
@@ -50,17 +53,17 @@ function parseLink(a, partCreator) {
             if (href === a.textContent) {
                 return partCreator.plain(a.textContent);
             } else {
-                return partCreator.plain(`[${a.textContent}](${href})`);
+                return partCreator.plain(`[${a.textContent.replace(/[[\\\]]/g, c => "\\" + c)}](${href})`);
             }
         }
     }
 }
 
-function parseCodeBlock(n, partCreator) {
+function parseCodeBlock(n: HTMLElement, partCreator: PartCreator) {
     const parts = [];
     let language = "";
     if (n.firstChild && n.firstChild.nodeName === "CODE") {
-        for (const className of n.firstChild.classList) {
+        for (const className of (<HTMLElement>n.firstChild).classList) {
             if (className.startsWith("language-")) {
                 language = className.substr("language-".length);
                 break;
@@ -77,12 +80,17 @@ function parseCodeBlock(n, partCreator) {
     return parts;
 }
 
-function parseHeader(el, partCreator) {
+function parseHeader(el: HTMLElement, partCreator: PartCreator) {
     const depth = parseInt(el.nodeName.substr(1), 10);
     return partCreator.plain("#".repeat(depth) + " ");
 }
 
-function parseElement(n, partCreator, lastNode, state) {
+interface IState {
+    listIndex: number[];
+    listDepth?: number;
+}
+
+function parseElement(n: HTMLElement, partCreator: PartCreator, lastNode: HTMLElement | undefined, state: IState) {
     switch (n.nodeName) {
         case "H1":
         case "H2":
@@ -92,7 +100,7 @@ function parseElement(n, partCreator, lastNode, state) {
         case "H6":
             return parseHeader(n, partCreator);
         case "A":
-            return parseLink(n, partCreator);
+            return parseLink(<HTMLAnchorElement>n, partCreator);
         case "BR":
             return partCreator.newline();
         case "EM":
@@ -123,11 +131,11 @@ function parseElement(n, partCreator, lastNode, state) {
             break;
         }
         case "OL":
-            state.listIndex.push(n.start || 1);
-            // fallthrough
+            state.listIndex.push((<HTMLOListElement>n).start || 1);
+            /* falls through */
         case "UL":
             state.listDepth = (state.listDepth || 0) + 1;
-            // fallthrough
+            /* falls through */
         default:
             // don't textify block nodes we'll descend into
             if (!checkDescendInto(n)) {
@@ -174,7 +182,7 @@ function prefixQuoteLines(isFirstNode, parts, partCreator) {
     }
 }
 
-function parseHtmlMessage(html, partCreator, isQuotedMessage) {
+function parseHtmlMessage(html: string, partCreator: PartCreator, isQuotedMessage: boolean) {
     // no nodes from parsing here should be inserted in the document,
     // as scripts in event handlers, etc would be executed then.
     // we're only taking text, so that is fine
@@ -182,7 +190,7 @@ function parseHtmlMessage(html, partCreator, isQuotedMessage) {
     const parts = [];
     let lastNode;
     let inQuote = isQuotedMessage;
-    const state = {
+    const state: IState = {
         listIndex: [],
     };
 
@@ -236,7 +244,7 @@ function parseHtmlMessage(html, partCreator, isQuotedMessage) {
                 break;
             case "OL":
                 state.listIndex.pop();
-                // fallthrough
+                /* falls through */
             case "UL":
                 state.listDepth -= 1;
                 break;
@@ -249,9 +257,9 @@ function parseHtmlMessage(html, partCreator, isQuotedMessage) {
     return parts;
 }
 
-export function parsePlainTextMessage(body, partCreator, isQuotedMessage) {
+export function parsePlainTextMessage(body: string, partCreator: PartCreator, isQuotedMessage: boolean) {
     const lines = body.split(/\r\n|\r|\n/g); // split on any new-line combination not just \n, collapses \r\n
-    const parts = lines.reduce((parts, line, i) => {
+    return lines.reduce((parts, line, i) => {
         if (isQuotedMessage) {
             parts.push(partCreator.plain(QUOTE_LINE_PREFIX));
         }
@@ -262,10 +270,9 @@ export function parsePlainTextMessage(body, partCreator, isQuotedMessage) {
         }
         return parts;
     }, []);
-    return parts;
 }
 
-export function parseEvent(event, partCreator, {isQuotedMessage = false} = {}) {
+export function parseEvent(event: MatrixEvent, partCreator: PartCreator, {isQuotedMessage = false} = {}) {
     const content = event.getContent();
     let parts;
     if (content.format === "org.matrix.custom.html") {
diff --git a/src/editor/serialize.js b/src/editor/serialize.ts
similarity index 78%
rename from src/editor/serialize.js
rename to src/editor/serialize.ts
index ba380f2809..4d0b8cd03a 100644
--- a/src/editor/serialize.js
+++ b/src/editor/serialize.ts
@@ -1,6 +1,6 @@
 /*
 Copyright 2019 New Vector Ltd
-Copyright 2019 The Matrix.org Foundation C.I.C.
+Copyright 2019, 2020 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -17,8 +17,9 @@ limitations under the License.
 
 import Markdown from '../Markdown';
 import {makeGenericPermalink} from "../utils/permalinks/Permalinks";
+import EditorModel from "./model";
 
-export function mdSerialize(model) {
+export function mdSerialize(model: EditorModel) {
     return model.parts.reduce((html, part) => {
         switch (part.type) {
             case "newline":
@@ -30,12 +31,12 @@ export function mdSerialize(model) {
                 return html + part.text;
             case "room-pill":
             case "user-pill":
-                return html + `[${part.text}](${makeGenericPermalink(part.resourceId)})`;
+                return html + `[${part.text.replace(/[[\\\]]/g, c => "\\" + c)}](${makeGenericPermalink(part.resourceId)})`;
         }
     }, "");
 }
 
-export function htmlSerializeIfNeeded(model, {forceHTML = false} = {}) {
+export function htmlSerializeIfNeeded(model: EditorModel, {forceHTML = false} = {}) {
     const md = mdSerialize(model);
     const parser = new Markdown(md);
     if (!parser.isPlainText() || forceHTML) {
@@ -43,7 +44,7 @@ export function htmlSerializeIfNeeded(model, {forceHTML = false} = {}) {
     }
 }
 
-export function textSerialize(model) {
+export function textSerialize(model: EditorModel) {
     return model.parts.reduce((text, part) => {
         switch (part.type) {
             case "newline":
@@ -60,11 +61,11 @@ export function textSerialize(model) {
     }, "");
 }
 
-export function containsEmote(model) {
+export function containsEmote(model: EditorModel) {
     return startsWith(model, "/me ");
 }
 
-export function startsWith(model, prefix) {
+export function startsWith(model: EditorModel, prefix: string) {
     const firstPart = model.parts[0];
     // part type will be "plain" while editing,
     // and "command" while composing a message.
@@ -73,18 +74,18 @@ export function startsWith(model, prefix) {
         firstPart.text.startsWith(prefix);
 }
 
-export function stripEmoteCommand(model) {
+export function stripEmoteCommand(model: EditorModel) {
     // trim "/me "
     return stripPrefix(model, "/me ");
 }
 
-export function stripPrefix(model, prefix) {
+export function stripPrefix(model: EditorModel, prefix: string) {
     model = model.clone();
     model.removeText({index: 0, offset: 0}, prefix.length);
     return model;
 }
 
-export function unescapeMessage(model) {
+export function unescapeMessage(model: EditorModel) {
     const {parts} = model;
     if (parts.length) {
         const firstPart = parts[0];
diff --git a/test/editor/deserialize-test.js b/test/editor/deserialize-test.js
index 1c58a6c40b..2bd5d7e4c6 100644
--- a/test/editor/deserialize-test.js
+++ b/test/editor/deserialize-test.js
@@ -148,6 +148,30 @@ describe('editor/deserialize', function() {
             expect(parts[1]).toStrictEqual({type: "user-pill", text: "Alice", resourceId: "@alice:hs.tld"});
             expect(parts[2]).toStrictEqual({type: "plain", text: "!"});
         });
+        it('user pill with displayname containing backslash', function() {
+            const html = "Hi <a href=\"https://matrix.to/#/@alice:hs.tld\">Alice\\</a>!";
+            const parts = normalize(parseEvent(htmlMessage(html), createPartCreator()));
+            expect(parts.length).toBe(3);
+            expect(parts[0]).toStrictEqual({type: "plain", text: "Hi "});
+            expect(parts[1]).toStrictEqual({type: "user-pill", text: "Alice\\", resourceId: "@alice:hs.tld"});
+            expect(parts[2]).toStrictEqual({type: "plain", text: "!"});
+        });
+        it('user pill with displayname containing opening square bracket', function() {
+            const html = "Hi <a href=\"https://matrix.to/#/@alice:hs.tld\">Alice[[</a>!";
+            const parts = normalize(parseEvent(htmlMessage(html), createPartCreator()));
+            expect(parts.length).toBe(3);
+            expect(parts[0]).toStrictEqual({type: "plain", text: "Hi "});
+            expect(parts[1]).toStrictEqual({type: "user-pill", text: "Alice[[", resourceId: "@alice:hs.tld"});
+            expect(parts[2]).toStrictEqual({type: "plain", text: "!"});
+        });
+        it('user pill with displayname containing closing square bracket', function() {
+            const html = "Hi <a href=\"https://matrix.to/#/@alice:hs.tld\">Alice]</a>!";
+            const parts = normalize(parseEvent(htmlMessage(html), createPartCreator()));
+            expect(parts.length).toBe(3);
+            expect(parts[0]).toStrictEqual({type: "plain", text: "Hi "});
+            expect(parts[1]).toStrictEqual({type: "user-pill", text: "Alice]", resourceId: "@alice:hs.tld"});
+            expect(parts[2]).toStrictEqual({type: "plain", text: "!"});
+        });
         it('room pill', function() {
             const html = "Try <a href=\"https://matrix.to/#/#room:hs.tld\">#room:hs.tld</a>?";
             const parts = normalize(parseEvent(htmlMessage(html), createPartCreator()));
diff --git a/test/editor/serialize-test.js b/test/editor/serialize-test.js
index 7517e46437..bd26ae91bb 100644
--- a/test/editor/serialize-test.js
+++ b/test/editor/serialize-test.js
@@ -43,4 +43,22 @@ describe('editor/serialize', function() {
         const html = htmlSerializeIfNeeded(model, {});
         expect(html).toBe("<em>hello</em> world");
     });
+    it('displaynames ending in a backslash work', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.userPill("Displayname\\", "@user:server")]);
+        const html = htmlSerializeIfNeeded(model, {});
+        expect(html).toBe("<a href=\"https://matrix.to/#/@user:server\">Displayname\\</a>");
+    });
+    it('displaynames containing an opening square bracket work', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.userPill("Displayname[[", "@user:server")]);
+        const html = htmlSerializeIfNeeded(model, {});
+        expect(html).toBe("<a href=\"https://matrix.to/#/@user:server\">Displayname[[</a>");
+    });
+    it('displaynames containing a closing square bracket work', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.userPill("Displayname]", "@user:server")]);
+        const html = htmlSerializeIfNeeded(model, {});
+        expect(html).toBe("<a href=\"https://matrix.to/#/@user:server\">Displayname]</a>");
+    });
 });