diff --git a/packages/theme/src/types.ts b/packages/theme/src/types.ts
index 143ccbabaa..8f71ce4292 100644
--- a/packages/theme/src/types.ts
+++ b/packages/theme/src/types.ts
@@ -104,3 +104,13 @@ export type PageTheme = {
   backgroundImage: string;
   fontColor: string;
 };
+
+/**
+ * Backstage specific additions to the material-ui theme.
+ *
+ * @public
+ */
+export type BackstageThemeAdditions = {
+  page: PageTheme;
+  getPageTheme: (selector: PageThemeSelector) => PageTheme;
+};
diff --git a/packages/theme/src/v4/types.ts b/packages/theme/src/v4/types.ts
index 7a292fe0a1..e21ced6e94 100644
--- a/packages/theme/src/v4/types.ts
+++ b/packages/theme/src/v4/types.ts
@@ -21,6 +21,7 @@ import {
 } from '@material-ui/core/styles/createPalette';
 import {
   BackstagePaletteAdditions,
+  BackstageThemeAdditions,
   PageTheme,
   PageThemeSelector,
 } from '../types';
@@ -93,13 +94,7 @@ declare module '@material-ui/core/styles/createPalette' {
 }
 
 declare module '@material-ui/core/styles/createTheme' {
-  interface Theme {
-    page: PageTheme;
-    getPageTheme: (selector: PageThemeSelector) => PageTheme;
-  }
+  interface Theme extends BackstageThemeAdditions {}
 
-  interface ThemeOptions {
-    page: PageTheme;
-    getPageTheme: (selector: PageThemeSelector) => PageTheme;
-  }
+  interface ThemeOptions extends BackstageThemeAdditions {}
 }
diff --git a/packages/theme/src/v5/types.ts b/packages/theme/src/v5/types.ts
index d1ffdf2e80..d3cf97411d 100644
--- a/packages/theme/src/v5/types.ts
+++ b/packages/theme/src/v5/types.ts
@@ -14,11 +14,7 @@
  * limitations under the License.
  */
 
-import {
-  BackstagePaletteAdditions,
-  PageTheme,
-  PageThemeSelector,
-} from '../types';
+import { BackstagePaletteAdditions, BackstageThemeAdditions } from '../types';
 
 declare module '@mui/material/styles/createPalette' {
   interface Palette extends BackstagePaletteAdditions {}
@@ -27,15 +23,9 @@ declare module '@mui/material/styles/createPalette' {
 }
 
 declare module '@mui/material/styles/createTheme' {
-  interface Theme {
-    pageTheme: PageTheme;
-    getPageTheme: (selector: PageThemeSelector) => PageTheme;
-  }
+  interface Theme extends BackstageThemeAdditions {}
 
-  interface ThemeOptions {
-    pageTheme: PageTheme;
-    getPageTheme: (selector: PageThemeSelector) => PageTheme;
-  }
+  interface ThemeOptions extends BackstageThemeAdditions {}
 }
 
 // This is a workaround for missing methods in React 17 that MUI v5 depends on