diff --git a/frontend/src/components/Toolbar.tsx b/frontend/src/components/Toolbar.tsx
index 47f00939ffc..3225a161e81 100644
--- a/frontend/src/components/Toolbar.tsx
+++ b/frontend/src/components/Toolbar.tsx
@@ -106,7 +106,7 @@ export interface ToolbarProps {
 
 class Toolbar extends React.Component<ToolbarProps> {
 
-  public render(): JSX.Element {
+  public render(): JSX.Element | null {
     const currentPage = this.props.breadcrumbs.length ?
       this.props.breadcrumbs[this.props.breadcrumbs.length - 1].displayName : '';
     const breadcrumbs = this.props.breadcrumbs.slice(0, this.props.breadcrumbs.length - 1);
diff --git a/frontend/src/pages/404.tsx b/frontend/src/pages/404.tsx
index 235c4caadaf..e747feabfe9 100644
--- a/frontend/src/pages/404.tsx
+++ b/frontend/src/pages/404.tsx
@@ -27,7 +27,7 @@ export default class Page404 extends Page<{}, {}> {
     return;
   }
 
-  public render() {
+  public render(): JSX.Element {
     return (
       <div style={{ margin: '100px auto', textAlign: 'center' }}>
         <div style={{ color: '#aaa', fontSize: 50, fontWeight: 'bold' }}>404</div>