diff --git a/docs/pages/material-ui/api/input-label.json b/docs/pages/material-ui/api/input-label.json
index 65861580971e2f..716c178dcf478a 100644
--- a/docs/pages/material-ui/api/input-label.json
+++ b/docs/pages/material-ui/api/input-label.json
@@ -16,7 +16,10 @@
     "required": { "type": { "name": "bool" } },
     "shrink": { "type": { "name": "bool" } },
     "size": {
-      "type": { "name": "enum", "description": "'normal'<br>&#124;&nbsp;'small'" },
+      "type": {
+        "name": "union",
+        "description": "'normal'<br>&#124;&nbsp;'small'<br>&#124;&nbsp;string"
+      },
       "default": "'normal'"
     },
     "sx": {
diff --git a/packages/mui-material/src/InputLabel/InputLabel.d.ts b/packages/mui-material/src/InputLabel/InputLabel.d.ts
index 285ad1f64cb952..e15cdc45fe8972 100644
--- a/packages/mui-material/src/InputLabel/InputLabel.d.ts
+++ b/packages/mui-material/src/InputLabel/InputLabel.d.ts
@@ -1,10 +1,13 @@
 import * as React from 'react';
 import { SxProps } from '@mui/system';
+import { OverridableStringUnion } from '@mui/types';
 import { InternalStandardProps as StandardProps } from '..';
 import { FormLabelProps } from '../FormLabel';
 import { Theme } from '../styles';
 import { InputLabelClasses } from './inputLabelClasses';
 
+export interface InputLabelPropsSizeOverrides {}
+
 export interface InputLabelProps extends StandardProps<FormLabelProps> {
   /**
    * The content of the component.
@@ -49,7 +52,7 @@ export interface InputLabelProps extends StandardProps<FormLabelProps> {
    * The size of the component.
    * @default 'normal'
    */
-  size?: 'small' | 'normal';
+  size?: OverridableStringUnion<'small' | 'normal', InputLabelPropsSizeOverrides>;
   /**
    * The system prop that allows defining system overrides as well as additional CSS styles.
    */
diff --git a/packages/mui-material/src/InputLabel/InputLabel.js b/packages/mui-material/src/InputLabel/InputLabel.js
index a6af7ad1b3c423..5318af7bd25fc2 100644
--- a/packages/mui-material/src/InputLabel/InputLabel.js
+++ b/packages/mui-material/src/InputLabel/InputLabel.js
@@ -224,7 +224,10 @@ InputLabel.propTypes /* remove-proptypes */ = {
    * The size of the component.
    * @default 'normal'
    */
-  size: PropTypes.oneOf(['normal', 'small']),
+  size: PropTypes /* @typescript-to-proptypes-ignore */.oneOfType([
+    PropTypes.oneOf(['normal', 'small']),
+    PropTypes.string,
+  ]),
   /**
    * The system prop that allows defining system overrides as well as additional CSS styles.
    */
diff --git a/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.spec.tsx b/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.spec.tsx
new file mode 100644
index 00000000000000..42d25f1922ff95
--- /dev/null
+++ b/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.spec.tsx
@@ -0,0 +1,13 @@
+import * as React from 'react';
+import InputLabel from '@mui/material/InputLabel';
+
+declare module '@mui/material/InputLabel' {
+  interface InputLabelPropsSizeOverrides {
+    customSize: true;
+  }
+}
+
+<InputLabel size="customSize" />;
+
+// @ts-expect-error unknown size
+<InputLabel size="foo" />;
diff --git a/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.tsconfig.json b/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.tsconfig.json
new file mode 100644
index 00000000000000..f53a33cae0908f
--- /dev/null
+++ b/packages/mui-material/test/typescript/moduleAugmentation/InputLabelCustomProps.tsconfig.json
@@ -0,0 +1,4 @@
+{
+  "extends": "../../../../../tsconfig",
+  "files": ["InputLabelCustomProps.spec.tsx"]
+}