diff --git a/src/components/structures/RoomView.tsx b/src/components/structures/RoomView.tsx
index e2614cb2df3..8e4d7210447 100644
--- a/src/components/structures/RoomView.tsx
+++ b/src/components/structures/RoomView.tsx
@@ -2342,7 +2342,7 @@ export class RoomView extends React.Component<IRoomProps, IRoomState> {
 
         const showChatEffects = SettingsStore.getValue("showChatEffects");
 
-        let mainSplitBody: React.ReactFragment;
+        let mainSplitBody: JSX.Element;
         let mainSplitContentClassName: string;
         // Decide what to show in the main split
         switch (this.state.mainSplitContentType) {
diff --git a/src/components/structures/UploadBar.tsx b/src/components/structures/UploadBar.tsx
index c87ad4754f9..6034bf690de 100644
--- a/src/components/structures/UploadBar.tsx
+++ b/src/components/structures/UploadBar.tsx
@@ -114,7 +114,7 @@ export default class UploadBar extends React.PureComponent<IProps, IState> {
             count: this.state.countFiles - 1,
         });
 
-        const uploadSize = filesize(this.state.currentTotal!);
+        const uploadSize = filesize(this.state.currentTotal!) as string;
         return (
             <div className="mx_UploadBar">
                 <div className="mx_UploadBar_filename">
diff --git a/src/components/views/dialogs/ChangelogDialog.tsx b/src/components/views/dialogs/ChangelogDialog.tsx
index 8321cc40f49..845698cc315 100644
--- a/src/components/views/dialogs/ChangelogDialog.tsx
+++ b/src/components/views/dialogs/ChangelogDialog.tsx
@@ -93,7 +93,7 @@ export default class ChangelogDialog extends React.Component<IProps, State> {
                 content = <Spinner key={repo} />;
             } else if (typeof this.state[repo] === "string") {
                 content = _t("Unable to load commit detail: %(msg)s", {
-                    msg: this.state[repo],
+                    msg: this.state[repo] as string,
                 });
             } else {
                 content = (this.state[repo] as Commit[]).map(this.elementsForCommit);
diff --git a/src/components/views/dialogs/UploadConfirmDialog.tsx b/src/components/views/dialogs/UploadConfirmDialog.tsx
index 584015e1603..526e02efbb8 100644
--- a/src/components/views/dialogs/UploadConfirmDialog.tsx
+++ b/src/components/views/dialogs/UploadConfirmDialog.tsx
@@ -115,7 +115,7 @@ export default class UploadConfirmDialog extends React.Component<IProps> {
                             {preview && <div>{preview}</div>}
                             <div id={fileId}>
                                 {placeholder}
-                                {this.props.file.name} ({filesize(this.props.file.size)})
+                                {this.props.file.name} ({filesize(this.props.file.size) as string})
                             </div>
                         </div>
                     </div>
diff --git a/src/components/views/dialogs/UploadFailureDialog.tsx b/src/components/views/dialogs/UploadFailureDialog.tsx
index 2bec57dd0d9..43e7af51684 100644
--- a/src/components/views/dialogs/UploadFailureDialog.tsx
+++ b/src/components/views/dialogs/UploadFailureDialog.tsx
@@ -52,8 +52,8 @@ export default class UploadFailureDialog extends React.Component<IProps> {
                 "This file is <b>too large</b> to upload. " +
                     "The file size limit is %(limit)s but this file is %(sizeOfThisFile)s.",
                 {
-                    limit: filesize(this.props.contentMessages.getUploadLimit()),
-                    sizeOfThisFile: filesize(this.props.badFiles[0].size),
+                    limit: filesize(this.props.contentMessages.getUploadLimit()) as string,
+                    sizeOfThisFile: filesize(this.props.badFiles[0].size) as string,
                 },
                 {
                     b: (sub) => <b>{sub}</b>,
@@ -71,7 +71,7 @@ export default class UploadFailureDialog extends React.Component<IProps> {
             message = _t(
                 "These files are <b>too large</b> to upload. " + "The file size limit is %(limit)s.",
                 {
-                    limit: filesize(this.props.contentMessages.getUploadLimit()),
+                    limit: filesize(this.props.contentMessages.getUploadLimit()) as string,
                 },
                 {
                     b: (sub) => <b>{sub}</b>,
@@ -89,7 +89,7 @@ export default class UploadFailureDialog extends React.Component<IProps> {
             message = _t(
                 "Some files are <b>too large</b> to be uploaded. " + "The file size limit is %(limit)s.",
                 {
-                    limit: filesize(this.props.contentMessages.getUploadLimit()),
+                    limit: filesize(this.props.contentMessages.getUploadLimit()) as string,
                 },
                 {
                     b: (sub) => <b>{sub}</b>,
diff --git a/src/components/views/messages/MFileBody.tsx b/src/components/views/messages/MFileBody.tsx
index b90f02c2cd7..1fc080b5905 100644
--- a/src/components/views/messages/MFileBody.tsx
+++ b/src/components/views/messages/MFileBody.tsx
@@ -350,7 +350,7 @@ export default class MFileBody extends React.Component<IProps, IState> {
                             </a>
                             {this.context.timelineRenderingType === TimelineRenderingType.File && (
                                 <div className="mx_MImageBody_size">
-                                    {this.content.info?.size ? filesize(this.content.info.size) : ""}
+                                    {this.content.info?.size ? (filesize(this.content.info.size) as string) : ""}
                                 </div>
                             )}
                         </div>
diff --git a/src/languageHandler.tsx b/src/languageHandler.tsx
index ec37d329657..dfc84e11b25 100644
--- a/src/languageHandler.tsx
+++ b/src/languageHandler.tsx
@@ -384,7 +384,7 @@ export function replaceByRegexes(text: string, mapping: IVariables | Tags): stri
     }
 
     if (shouldWrapInSpan) {
-        return React.createElement("span", null, ...output);
+        return React.createElement("span", null, ...(output as Array<number | string | React.ReactNode>));
     } else {
         return output.join("");
     }
diff --git a/test/i18n-test/languageHandler-test.tsx b/test/i18n-test/languageHandler-test.tsx
index 66c88fe5679..0368fe99602 100644
--- a/test/i18n-test/languageHandler-test.tsx
+++ b/test/i18n-test/languageHandler-test.tsx
@@ -23,6 +23,8 @@ import {
     setLanguage,
     setMissingEntryGenerator,
     substitute,
+    IVariables,
+    Tags,
 } from "../../src/languageHandler";
 import { stubClient } from "../test-utils";
 
@@ -34,7 +36,7 @@ describe("languageHandler", function () {
     const plurals = "and %(count)s others...";
     const variableSub = "You are now ignoring %(userId)s";
 
-    type TestCase = [string, string, Record<string, unknown>, Record<string, unknown> | undefined, TranslatedString];
+    type TestCase = [string, string, IVariables, Tags | undefined, TranslatedString];
     const testCasesEn: TestCase[] = [
         // description of the test case, translationString, variables, tags, expected result
         ["translates a basic string", basicString, {}, undefined, "Rooms"],