diff --git a/package.json b/package.json
index 7ba69c4272..0e1909f3e3 100644
--- a/package.json
+++ b/package.json
@@ -117,6 +117,7 @@
     "@babel/register": "^7.7.4",
     "@peculiar/webcrypto": "^1.0.22",
     "@types/classnames": "^2.2.10",
+    "@types/modernizr": "^3.5.3",
     "@types/react": "16.9",
     "babel-eslint": "^10.0.3",
     "babel-jest": "^24.9.0",
diff --git a/src/@types/global.d.ts b/src/@types/global.d.ts
new file mode 100644
index 0000000000..1931c0b1d0
--- /dev/null
+++ b/src/@types/global.d.ts
@@ -0,0 +1,40 @@
+/*
+Copyright 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.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import * as ModernizrStatic from "modernizr";
+
+declare global {
+    interface Window {
+        Modernizr: ModernizrStatic;
+        Olm: {
+            init: () => Promise<void>;
+        };
+    }
+
+    // workaround for https://github.com/microsoft/TypeScript/issues/30933
+    interface ObjectConstructor {
+        fromEntries?(xs: [string|number|symbol, any][]): object
+    }
+
+    interface Document {
+        // https://developer.mozilla.org/en-US/docs/Web/API/Document/hasStorageAccess
+        hasStorageAccess?: () => Promise<boolean>;
+    }
+
+    interface StorageEstimate {
+        usageDetails?: {[key: string]: number};
+    }
+}
diff --git a/src/rageshake/submit-rageshake.js b/src/rageshake/submit-rageshake.ts
similarity index 85%
rename from src/rageshake/submit-rageshake.js
rename to src/rageshake/submit-rageshake.ts
index 55c89427c5..921f3fbf40 100644
--- a/src/rageshake/submit-rageshake.js
+++ b/src/rageshake/submit-rageshake.ts
@@ -33,6 +33,13 @@ if (!TextEncoder) {
     TextEncoder = TextEncodingUtf8.TextEncoder;
 }
 
+interface IOpts {
+    label?: string;
+    userText?: string;
+    sendLogs?: boolean;
+    progressCallback?: (string) => void;
+}
+
 /**
  * Send a bug report.
  *
@@ -48,7 +55,7 @@ if (!TextEncoder) {
  *
  * @return {Promise} Resolved when the bug report is sent.
  */
-export default async function sendBugReport(bugReportEndpoint, opts) {
+export default async function sendBugReport(bugReportEndpoint: string, opts: IOpts) {
     if (!bugReportEndpoint) {
         throw new Error("No bug report endpoint has been set.");
     }
@@ -70,13 +77,13 @@ export default async function sendBugReport(bugReportEndpoint, opts) {
     let installedPWA = "UNKNOWN";
     try {
         // Known to work at least for desktop Chrome
-        installedPWA = window.matchMedia('(display-mode: standalone)').matches;
-    } catch (e) { }
+        installedPWA = String(window.matchMedia('(display-mode: standalone)').matches);
+    } catch (e) {}
 
     let touchInput = "UNKNOWN";
     try {
         // MDN claims broad support across browsers
-        touchInput = window.matchMedia('(pointer: coarse)').matches;
+        touchInput = String(window.matchMedia('(pointer: coarse)').matches);
     } catch (e) { }
 
     const client = MatrixClientPeg.get();
@@ -118,21 +125,21 @@ export default async function sendBugReport(bugReportEndpoint, opts) {
     // add storage persistence/quota information
     if (navigator.storage && navigator.storage.persisted) {
         try {
-            body.append("storageManager_persisted", await navigator.storage.persisted());
+            body.append("storageManager_persisted", String(await navigator.storage.persisted()));
         } catch (e) {}
     } else if (document.hasStorageAccess) { // Safari
         try {
-            body.append("storageManager_persisted", await document.hasStorageAccess());
+            body.append("storageManager_persisted", String(await document.hasStorageAccess()));
         } catch (e) {}
     }
     if (navigator.storage && navigator.storage.estimate) {
         try {
             const estimate = await navigator.storage.estimate();
-            body.append("storageManager_quota", estimate.quota);
-            body.append("storageManager_usage", estimate.usage);
+            body.append("storageManager_quota", String(estimate.quota));
+            body.append("storageManager_usage", String(estimate.usage));
             if (estimate.usageDetails) {
                 Object.keys(estimate.usageDetails).forEach(k => {
-                    body.append(`storageManager_usage_${k}`, estimate.usageDetails[k]);
+                    body.append(`storageManager_usage_${k}`, String(estimate.usageDetails[k]));
                 });
             }
         } catch (e) {}
@@ -163,7 +170,7 @@ export default async function sendBugReport(bugReportEndpoint, opts) {
     await _submitReport(bugReportEndpoint, body, progressCallback);
 }
 
-function _submitReport(endpoint, body, progressCallback) {
+function _submitReport(endpoint: string, body: FormData, progressCallback: (string) => void) {
     return new Promise((resolve, reject) => {
         const req = new XMLHttpRequest();
         req.open("POST", endpoint);
diff --git a/yarn.lock b/yarn.lock
index c42828e461..c601e37340 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1257,6 +1257,11 @@
   resolved "https://registry.yarnpkg.com/@types/minimatch/-/minimatch-3.0.3.tgz#3dca0e3f33b200fc7d1139c0cd96c1268cadfd9d"
   integrity sha512-tHq6qdbT9U1IRSGf14CL0pUlULksvY9OZ+5eEgl1N7t+OA3tGvNpxJCzuKQlsNgCVwbAs670L1vcVQi8j9HjnA==
 
+"@types/modernizr@^3.5.3":
+  version "3.5.3"
+  resolved "https://registry.yarnpkg.com/@types/modernizr/-/modernizr-3.5.3.tgz#8ef99e6252191c1d88647809109dc29884ba6d7a"
+  integrity sha512-jhMOZSS0UGYTS9pqvt6q3wtT3uvOSve5piTEmTMx3zzTuBLvSIMxSIBIc3d5lajVD5h4xc41AMZD2M5orN3PxA==
+
 "@types/node@*":
   version "13.11.0"
   resolved "https://registry.yarnpkg.com/@types/node/-/node-13.11.0.tgz#390ea202539c61c8fa6ba4428b57e05bc36dc47b"