diff --git a/knip.ts b/knip.ts
index e129c11481..dd283a0580 100644
--- a/knip.ts
+++ b/knip.ts
@@ -42,6 +42,13 @@ export default {
         "util",
         // Embedded into webapp
         "@element-hq/element-call-embedded",
+
+        // Used by matrix-js-sdk, which means we have to include them as a
+        // dependency so that // we can run `tsc` (since we import the typescript
+        // source of js-sdk, rather than the transpiled and annotated JS like you
+        // would with a normal library).
+        "@types/content-type",
+        "@types/sdp-transform",
     ],
     ignoreBinaries: [
         // Used in scripts & workflows
diff --git a/package.json b/package.json
index aa21689838..6af83533a1 100644
--- a/package.json
+++ b/package.json
@@ -203,6 +203,7 @@
         "@testing-library/react": "^16.0.0",
         "@testing-library/user-event": "^14.5.2",
         "@types/commonmark": "^0.27.4",
+        "@types/content-type": "^1.1.9",
         "@types/counterpart": "^0.18.1",
         "@types/css-tree": "^2.3.8",
         "@types/diff-match-patch": "^1.0.32",
@@ -226,6 +227,7 @@
         "@types/react-dom": "19.1.7",
         "@types/react-transition-group": "^4.4.0",
         "@types/sanitize-html": "2.16.0",
+        "@types/sdp-transform": "^2.4.10",
         "@types/semver": "^7.5.8",
         "@types/tar-js": "^0.3.5",
         "@types/ua-parser-js": "^0.7.36",
diff --git a/src/@types/global.d.ts b/src/@types/global.d.ts
index 77e57e1434..a8f132c84b 100644
--- a/src/@types/global.d.ts
+++ b/src/@types/global.d.ts
@@ -71,6 +71,13 @@ type ElectronChannel =
     | "serverSupportedVersions";
 
 declare global {
+    // use `number` as the return type in all cases for globalThis.set{Interval,Timeout},
+    // so we don't accidentally use the methods on NodeJS.Timeout - they only exist in a subset of environments.
+    // The overload for clear{Interval,Timeout} is resolved as expected.
+    // We use `ReturnType<typeof setTimeout>` in the code to be agnostic of if this definition gets loaded.
+    function setInterval(handler: TimerHandler, timeout: number, ...arguments: any[]): number;
+    function setTimeout(handler: TimerHandler, timeout: number, ...arguments: any[]): number;
+
     interface Window {
         mxSendRageshake: (text: string, withLogs?: boolean) => void;
         matrixLogger: typeof logger;
diff --git a/yarn.lock b/yarn.lock
index 6237354a3c..043ab0c180 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3965,6 +3965,11 @@
   dependencies:
     "@types/node" "*"
 
+"@types/content-type@^1.1.9":
+  version "1.1.9"
+  resolved "https://registry.yarnpkg.com/@types/content-type/-/content-type-1.1.9.tgz#a0240a8141b33549ac0ca6847f4b801580012bca"
+  integrity sha512-Hq9IMnfekuOCsEmYl4QX2HBrT+XsfXiupfrLLY8Dcf3Puf4BkBOxSbWYTITSOQAhJoYPBez+b4MJRpIYL65z8A==
+
 "@types/counterpart@^0.18.1":
   version "0.18.4"
   resolved "https://registry.yarnpkg.com/@types/counterpart/-/counterpart-0.18.4.tgz#e3e331b7e0d5496873d417839f3b2bbcf555bb73"
@@ -4334,6 +4339,11 @@
   dependencies:
     htmlparser2 "^8.0.0"
 
+"@types/sdp-transform@^2.4.10":
+  version "2.4.10"
+  resolved "https://registry.yarnpkg.com/@types/sdp-transform/-/sdp-transform-2.4.10.tgz#f4e60fbc97f66527f221a3ae092be7c465c55f56"
+  integrity sha512-999diMTpgQGt+dj+tAEQNvBAJYkOip83NJn1RruqNmqeLYNZpQnUX/YrugR+ekXvdJ9pdkZtYg1jiM3mG3NhRg==
+
 "@types/seedrandom@^3.0.8":
   version "3.0.8"
   resolved "https://registry.yarnpkg.com/@types/seedrandom/-/seedrandom-3.0.8.tgz#61cc8ed88f93a3c31289c295e6df8ca40be42bdf"