diff --git a/.eslintrc.js b/.eslintrc.js
index 6795f11..e15d9d5 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -30,8 +30,9 @@ module.exports = {
             "prefer-promise-reject-errors": "off",
             "quotes": "off",
 
-            // We disable this while we're transitioning
             "@typescript-eslint/no-explicit-any": "off",
+            // We're okay with assertion errors when we ask for them
+            "@typescript-eslint/no-non-null-assertion": "off",
         },
     }],
 };
diff --git a/src/ipc.ts b/src/ipc.ts
index 717a701..f5e3f29 100644
--- a/src/ipc.ts
+++ b/src/ipc.ts
@@ -46,7 +46,7 @@ ipcMain.on('loudNotification', function(): void {
     }
 });
 
-let powerSaveBlockerId: number = null;
+let powerSaveBlockerId: number | null = null;
 ipcMain.on('app_onAction', function(_ev: IpcMainEvent, payload) {
     switch (payload.action) {
         case 'call_state': {
@@ -147,11 +147,11 @@ ipcMain.on('ipcCall', async function(_ev: IpcMainEvent, payload) {
 
         case 'getPickleKey':
             try {
-                ret = await keytar.getPassword("element.io", `${args[0]}|${args[1]}`);
+                ret = await keytar?.getPassword("element.io", `${args[0]}|${args[1]}`);
                 // migrate from riot.im (remove once we think there will no longer be
                 // logins from the time of riot.im)
                 if (ret === null) {
-                    ret = await keytar.getPassword("riot.im", `${args[0]}|${args[1]}`);
+                    ret = await keytar?.getPassword("riot.im", `${args[0]}|${args[1]}`);
                 }
             } catch (e) {
                 // if an error is thrown (e.g. keytar can't connect to the keychain),
@@ -163,7 +163,7 @@ ipcMain.on('ipcCall', async function(_ev: IpcMainEvent, payload) {
         case 'createPickleKey':
             try {
                 const pickleKey = await randomArray(32);
-                await keytar.setPassword("element.io", `${args[0]}|${args[1]}`, pickleKey);
+                await keytar?.setPassword("element.io", `${args[0]}|${args[1]}`, pickleKey);
                 ret = pickleKey;
             } catch (e) {
                 ret = null;
@@ -172,10 +172,10 @@ ipcMain.on('ipcCall', async function(_ev: IpcMainEvent, payload) {
 
         case 'destroyPickleKey':
             try {
-                await keytar.deletePassword("element.io", `${args[0]}|${args[1]}`);
+                await keytar?.deletePassword("element.io", `${args[0]}|${args[1]}`);
                 // migrate from riot.im (remove once we think there will no longer be
                 // logins from the time of riot.im)
-                await keytar.deletePassword("riot.im", `${args[0]}|${args[1]}`);
+                await keytar?.deletePassword("riot.im", `${args[0]}|${args[1]}`);
             } catch (e) {}
             break;
         case 'getDesktopCapturerSources':
diff --git a/src/keytar.ts b/src/keytar.ts
index 58d3436..c335774 100644
--- a/src/keytar.ts
+++ b/src/keytar.ts
@@ -21,7 +21,7 @@ try {
     // eslint-disable-next-line @typescript-eslint/no-var-requires
     keytar = require('keytar');
 } catch (e) {
-    if (e.code === "MODULE_NOT_FOUND") {
+    if ((<NodeJS.ErrnoException>e).code === "MODULE_NOT_FOUND") {
         console.log("Keytar isn't installed; secure key storage is disabled.");
     } else {
         console.warn("Keytar unexpected error:", e);
diff --git a/src/language-helper.ts b/src/language-helper.ts
index 47fe431..29189fe 100644
--- a/src/language-helper.ts
+++ b/src/language-helper.ts
@@ -27,7 +27,7 @@ export function _td(text: string): string {
 type SubstitutionValue = number | string;
 
 interface IVariables {
-    [key: string]: SubstitutionValue;
+    [key: string]: SubstitutionValue | undefined;
     count?: number;
 }
 
@@ -66,13 +66,13 @@ export function _t(text: string, variables: IVariables = {}): string {
 
 type Component = () => void;
 
-type TypedStore = Store<{ locale?: string | string[] }>;
+type TypedStore = Store<{ locale?: string[] }>;
 
 export class AppLocalization {
     private static readonly STORE_KEY = "locale";
 
     private readonly store: TypedStore;
-    private readonly localizedComponents: Set<Component>;
+    private readonly localizedComponents?: Set<Component>;
 
     constructor({ store, components = [] }: { store: TypedStore, components: Component[] }) {
         counterpart.registerTranslations("en", this.fetchTranslationJson("en_EN"));
@@ -86,7 +86,8 @@ export class AppLocalization {
         this.store = store;
         if (this.store.has(AppLocalization.STORE_KEY)) {
             const locales = this.store.get(AppLocalization.STORE_KEY);
-            this.setAppLocale(locales);
+            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+            this.setAppLocale(locales!);
         }
 
         this.resetLocalizedUI();
@@ -110,7 +111,7 @@ export class AppLocalization {
             return require(`./i18n/strings/${this.denormalize(locale)}.json`);
         } catch (e) {
             console.log(`Could not fetch translation json for locale: '${locale}'`, e);
-            return null;
+            return {};
         }
     }
 
@@ -138,7 +139,7 @@ export class AppLocalization {
 
     public resetLocalizedUI(): void {
         console.log("Resetting the UI components after locale change");
-        this.localizedComponents.forEach(componentSetup => {
+        this.localizedComponents?.forEach(componentSetup => {
             if (typeof componentSetup === "function") {
                 componentSetup();
             }
diff --git a/src/protocol.ts b/src/protocol.ts
index 7e3bd8b..1c79184 100644
--- a/src/protocol.ts
+++ b/src/protocol.ts
@@ -86,7 +86,7 @@ export function getProfileFromDeeplink(args: string[]): string | undefined {
     if (deeplinkUrl && deeplinkUrl.includes(SEARCH_PARAM)) {
         const parsedUrl = new URL(deeplinkUrl);
         if (parsedUrl.protocol === PROTOCOL) {
-            const ssoID = parsedUrl.searchParams.get(SEARCH_PARAM);
+            const ssoID = parsedUrl.searchParams.get(SEARCH_PARAM)!;
             const store = readStore();
             console.log("Forwarding to profile: ", store[ssoID]);
             return store[ssoID];
diff --git a/src/seshat.ts b/src/seshat.ts
index 49d48d3..77022b9 100644
--- a/src/seshat.ts
+++ b/src/seshat.ts
@@ -40,7 +40,7 @@ try {
     ReindexError = seshatModule.ReindexError;
     seshatSupported = true;
 } catch (e) {
-    if (e.code === "MODULE_NOT_FOUND") {
+    if ((<NodeJS.ErrnoException>e).code === "MODULE_NOT_FOUND") {
         console.log("Seshat isn't installed, event indexing is disabled.");
     } else {
         console.warn("Seshat unexpected error:", e);
@@ -49,7 +49,7 @@ try {
 
 const eventStorePath = path.join(app.getPath('userData'), 'EventStore');
 
-let eventIndex: SeshatType = null;
+let eventIndex: SeshatType | null = null;
 
 const seshatDefaultPassphrase = "DEFAULT_PASSPHRASE";
 async function getOrCreatePassphrase(key: string): Promise<string> {
@@ -66,9 +66,8 @@ async function getOrCreatePassphrase(key: string): Promise<string> {
         } catch (e) {
             console.log("Error getting the event index passphrase out of the secret store", e);
         }
-    } else {
-        return seshatDefaultPassphrase;
     }
+    return seshatDefaultPassphrase;
 }
 
 const deleteContents = async (p: string): Promise<void> => {
@@ -180,7 +179,7 @@ ipcMain.on('seshat', async function(_ev: IpcMainEvent, payload): Promise<void> {
 
         case 'addEventToIndex':
             try {
-                eventIndex.addEvent(args[0], args[1]);
+                eventIndex?.addEvent(args[0], args[1]);
             } catch (e) {
                 sendError(payload.id, e);
                 return;
@@ -189,7 +188,7 @@ ipcMain.on('seshat', async function(_ev: IpcMainEvent, payload): Promise<void> {
 
         case 'deleteEvent':
             try {
-                ret = await eventIndex.deleteEvent(args[0]);
+                ret = await eventIndex?.deleteEvent(args[0]);
             } catch (e) {
                 sendError(payload.id, e);
                 return;
@@ -198,7 +197,7 @@ ipcMain.on('seshat', async function(_ev: IpcMainEvent, payload): Promise<void> {
 
         case 'commitLiveEvents':
             try {
-                ret = await eventIndex.commit();
+                ret = await eventIndex?.commit();
             } catch (e) {
                 sendError(payload.id, e);
                 return;
@@ -207,7 +206,7 @@ ipcMain.on('seshat', async function(_ev: IpcMainEvent, payload): Promise<void> {
 
         case 'searchEventIndex':
             try {
-                ret = await eventIndex.search(args[0]);
+                ret = await eventIndex?.search(args[0]);
             } catch (e) {
                 sendError(payload.id, e);
                 return;
diff --git a/src/tray.ts b/src/tray.ts
index 6d95d30..e015238 100644
--- a/src/tray.ts
+++ b/src/tray.ts
@@ -22,7 +22,7 @@ import fs from "fs";
 
 import { _t } from "./language-helper";
 
-let trayIcon: Tray = null;
+let trayIcon: Tray | null = null;
 
 export function hasTray(): boolean {
     return (trayIcon !== null);
@@ -65,7 +65,7 @@ export function create(config: IConfig): void {
         if (!favicons || favicons.length <= 0 || !favicons[0].startsWith('data:')) {
             if (lastFavicon !== null) {
                 global.mainWindow.setIcon(defaultIcon);
-                trayIcon.setImage(defaultIcon);
+                trayIcon?.setImage(defaultIcon);
                 lastFavicon = null;
             }
             return;
@@ -88,12 +88,12 @@ export function create(config: IConfig): void {
             }
         }
 
-        trayIcon.setImage(newFavicon);
+        trayIcon?.setImage(newFavicon);
         global.mainWindow.setIcon(newFavicon);
     });
 
     global.mainWindow.webContents.on('page-title-updated', function(ev, title) {
-        trayIcon.setToolTip(title);
+        trayIcon?.setToolTip(title);
     });
 }
 
diff --git a/src/updater.ts b/src/updater.ts
index bb17efb..77fa401 100644
--- a/src/updater.ts
+++ b/src/updater.ts
@@ -70,6 +70,7 @@ export function start(updateBaseUrl: string): void {
             // I'm not even going to try to guess which feed style they'd use if they
             // implemented it on Linux, or if it would be different again.
             console.log('Auto update not supported on this platform');
+            return;
         }
 
         if (url) {
diff --git a/src/webcontents-handler.ts b/src/webcontents-handler.ts
index 2a9e2fd..b885431 100644
--- a/src/webcontents-handler.ts
+++ b/src/webcontents-handler.ts
@@ -50,7 +50,7 @@ function safeOpenURL(target: string): void {
     // (for instance, open /bin/sh does indeed open a terminal
     // with a shell, albeit with no arguments)
     const parsedUrl = url.parse(target);
-    if (PERMITTED_URL_SCHEMES.indexOf(parsedUrl.protocol) > -1) {
+    if (PERMITTED_URL_SCHEMES.includes(parsedUrl.protocol!)) {
         // explicitly use the URL re-assembled by the url library,
         // so we know the url parser has understood all the parts
         // of the input string
@@ -69,7 +69,7 @@ function onWindowOrNavigate(ev: Event, target: string): void {
 }
 
 function writeNativeImage(filePath: string, img: NativeImage): Promise<void> {
-    switch (filePath.split('.').pop().toLowerCase()) {
+    switch (filePath.split('.').pop()?.toLowerCase()) {
         case "jpg":
         case "jpeg":
             return fs.promises.writeFile(filePath, img.toJPEG(100));
@@ -181,7 +181,7 @@ function cutCopyPasteSelectContextMenus(params: ContextMenuParams): MenuItemCons
             options.push({
                 label: word,
                 click: (menuItem, browserWindow) => {
-                    browserWindow.webContents.replaceMisspelling(word);
+                    browserWindow?.webContents.replaceMisspelling(word);
                 },
             });
         });
@@ -190,7 +190,7 @@ function cutCopyPasteSelectContextMenus(params: ContextMenuParams): MenuItemCons
         }, {
             label: _t('Add to dictionary'),
             click: (menuItem, browserWindow) => {
-                browserWindow.webContents.session.addWordToSpellCheckerDictionary(params.misspelledWord);
+                browserWindow?.webContents.session.addWordToSpellCheckerDictionary(params.misspelledWord);
             },
         }, {
             type: 'separator',
@@ -251,8 +251,9 @@ function onEditableContextMenu(ev: Event, params: ContextMenuParams) {
 let userDownloadIndex = 0;
 const userDownloadMap = new Map<number, string>(); // Map from id to path
 ipcMain.on('userDownloadAction', function(ev: IpcMainEvent, { id, open = false }) {
-    if (open) {
-        shell.openPath(userDownloadMap.get(id));
+    const path = userDownloadMap.get(id);
+    if (open && path) {
+        shell.openPath(path);
     }
     userDownloadMap.delete(id);
 });
diff --git a/tsconfig.json b/tsconfig.json
index 0733089..1c42f2e 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -16,6 +16,7 @@
       "dom"
     ],
     "types": ["jest", "node"],
+    "strict": true
   },
   "include": [
     "./src/**/*.ts",