diff --git a/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.tsx b/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.tsx
index 3671ee60d1..5fbedd9654 100644
--- a/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.tsx
+++ b/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.tsx
@@ -1,10 +1,10 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import type { FieldsetLegendOwnerState, FieldsetLegendProps } from './FieldsetLegend.types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
 import { useFieldsetLegend } from './useFieldsetLegend';
 import { useFieldsetRootContext } from '../Root/FieldsetRootContext';
+import type { BaseUIComponentProps } from '../../utils/types';
 
 /**
  * Renders an element that labels the fieldset.
@@ -18,7 +18,7 @@ import { useFieldsetRootContext } from '../Root/FieldsetRootContext';
  * - [FieldsetLegend API](https://base-ui.netlify.app/components/react-fieldset/#api-reference-FieldsetLegend)
  */
 const FieldsetLegend = React.forwardRef(function FieldsetLegend(
-  props: FieldsetLegendProps,
+  props: FieldsetLegend.Props,
   forwardedRef: React.ForwardedRef<HTMLSpanElement>,
 ) {
   const { render, className, id, ...otherProps } = props;
@@ -27,7 +27,7 @@ const FieldsetLegend = React.forwardRef(function FieldsetLegend(
 
   const { disabled } = useFieldsetRootContext();
 
-  const ownerState: FieldsetLegendOwnerState = React.useMemo(
+  const ownerState: FieldsetLegend.OwnerState = React.useMemo(
     () => ({
       disabled: disabled ?? false,
     }),
@@ -46,6 +46,14 @@ const FieldsetLegend = React.forwardRef(function FieldsetLegend(
   return renderElement();
 });
 
+namespace FieldsetLegend {
+  export type OwnerState = {
+    disabled: boolean;
+  };
+
+  export interface Props extends BaseUIComponentProps<'span', OwnerState> {}
+}
+
 FieldsetLegend.propTypes /* remove-proptypes */ = {
   // ┌────────────────────────────── Warning ──────────────────────────────┐
   // │ These PropTypes are generated from the TypeScript type definitions. │
diff --git a/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.types.ts b/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.types.ts
deleted file mode 100644
index 1cb1ed5e18..0000000000
--- a/packages/mui-base/src/Fieldset/Legend/FieldsetLegend.types.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-import type { BaseUIComponentProps } from '../../utils/types';
-
-export type FieldsetLegendOwnerState = {
-  disabled: boolean;
-};
-
-export interface FieldsetLegendProps
-  extends BaseUIComponentProps<'span', FieldsetLegendOwnerState> {}
diff --git a/packages/mui-base/src/Fieldset/Legend/useFieldsetLegend.ts b/packages/mui-base/src/Fieldset/Legend/useFieldsetLegend.ts
index 37aefaa774..2d07e6032b 100644
--- a/packages/mui-base/src/Fieldset/Legend/useFieldsetLegend.ts
+++ b/packages/mui-base/src/Fieldset/Legend/useFieldsetLegend.ts
@@ -5,11 +5,7 @@ import { useId } from '../../utils/useId';
 import { useEnhancedEffect } from '../../utils/useEnhancedEffect';
 import { useFieldsetRootContext } from '../Root/FieldsetRootContext';
 
-interface UseFieldsetLegendParameters {
-  id?: string;
-}
-
-export function useFieldsetLegend(params: UseFieldsetLegendParameters) {
+export function useFieldsetLegend(params: useFieldsetLegend.Parameters) {
   const { id: idProp } = params;
 
   const { setLegendId } = useFieldsetRootContext();
@@ -38,3 +34,9 @@ export function useFieldsetLegend(params: UseFieldsetLegendParameters) {
     [getLegendProps],
   );
 }
+
+export namespace useFieldsetLegend {
+  export interface Parameters {
+    id?: string;
+  }
+}
diff --git a/packages/mui-base/src/Fieldset/Root/FieldsetRoot.tsx b/packages/mui-base/src/Fieldset/Root/FieldsetRoot.tsx
index ba657b9e3a..74a47b859b 100644
--- a/packages/mui-base/src/Fieldset/Root/FieldsetRoot.tsx
+++ b/packages/mui-base/src/Fieldset/Root/FieldsetRoot.tsx
@@ -1,10 +1,10 @@
 'use client';
 import * as React from 'react';
 import PropTypes from 'prop-types';
-import type { FieldsetRootOwnerState, FieldsetRootProps } from './FieldsetRoot.types';
 import { useComponentRenderer } from '../../utils/useComponentRenderer';
-import { FieldsetRootContext, type FieldsetRootContextValue } from './FieldsetRootContext';
+import { FieldsetRootContext } from './FieldsetRootContext';
 import { useFieldsetRoot } from './useFieldsetRoot';
+import type { BaseUIComponentProps } from '../../utils/types';
 
 /**
  * The foundation for building custom-styled fieldsets.
@@ -18,14 +18,14 @@ import { useFieldsetRoot } from './useFieldsetRoot';
  * - [FieldsetRoot API](https://base-ui.netlify.app/components/react-fieldset/#api-reference-FieldsetRoot)
  */
 const FieldsetRoot = React.forwardRef(function FieldsetRoot(
-  props: FieldsetRootProps,
+  props: FieldsetRoot.Props,
   forwardedRef: React.ForwardedRef<HTMLFieldSetElement>,
 ) {
   const { render, className, disabled = false, ...otherProps } = props;
 
   const { legendId, setLegendId, getRootProps } = useFieldsetRoot();
 
-  const ownerState: FieldsetRootOwnerState = React.useMemo(
+  const ownerState: FieldsetRoot.OwnerState = React.useMemo(
     () => ({
       disabled,
     }),
@@ -41,7 +41,7 @@ const FieldsetRoot = React.forwardRef(function FieldsetRoot(
     extraProps: otherProps,
   });
 
-  const contextValue: FieldsetRootContextValue = React.useMemo(
+  const contextValue: FieldsetRootContext = React.useMemo(
     () => ({
       legendId,
       setLegendId,
@@ -57,6 +57,14 @@ const FieldsetRoot = React.forwardRef(function FieldsetRoot(
   );
 });
 
+namespace FieldsetRoot {
+  export type OwnerState = {
+    disabled: boolean;
+  };
+
+  export interface Props extends BaseUIComponentProps<'fieldset', OwnerState> {}
+}
+
 FieldsetRoot.propTypes /* remove-proptypes */ = {
   // ┌────────────────────────────── Warning ──────────────────────────────┐
   // │ These PropTypes are generated from the TypeScript type definitions. │
diff --git a/packages/mui-base/src/Fieldset/Root/FieldsetRoot.types.ts b/packages/mui-base/src/Fieldset/Root/FieldsetRoot.types.ts
deleted file mode 100644
index 5405138555..0000000000
--- a/packages/mui-base/src/Fieldset/Root/FieldsetRoot.types.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-import type { BaseUIComponentProps } from '../../utils/types';
-
-export type FieldsetRootOwnerState = {
-  disabled: boolean;
-};
-
-export interface FieldsetRootProps
-  extends BaseUIComponentProps<'fieldset', FieldsetRootOwnerState> {}
diff --git a/packages/mui-base/src/Fieldset/Root/FieldsetRootContext.ts b/packages/mui-base/src/Fieldset/Root/FieldsetRootContext.ts
index 9692eae8b5..80dc08ea3c 100644
--- a/packages/mui-base/src/Fieldset/Root/FieldsetRootContext.ts
+++ b/packages/mui-base/src/Fieldset/Root/FieldsetRootContext.ts
@@ -1,13 +1,13 @@
 'use client';
 import * as React from 'react';
 
-export interface FieldsetRootContextValue {
+export interface FieldsetRootContext {
   legendId: string | undefined;
   setLegendId: React.Dispatch<React.SetStateAction<string | undefined>>;
   disabled: boolean | undefined;
 }
 
-export const FieldsetRootContext = React.createContext<FieldsetRootContextValue>({
+export const FieldsetRootContext = React.createContext<FieldsetRootContext>({
   legendId: undefined,
   setLegendId: () => {},
   disabled: undefined,
diff --git a/packages/mui-base/src/Fieldset/index.barrel.ts b/packages/mui-base/src/Fieldset/index.barrel.ts
index bd5416640a..b5a4cbaf40 100644
--- a/packages/mui-base/src/Fieldset/index.barrel.ts
+++ b/packages/mui-base/src/Fieldset/index.barrel.ts
@@ -1,5 +1,2 @@
 export * from './Root/FieldsetRoot';
 export * from './Legend/FieldsetLegend';
-
-export type * from './Root/FieldsetRoot.types';
-export type * from './Legend/FieldsetLegend.types';
diff --git a/packages/mui-base/src/Fieldset/index.ts b/packages/mui-base/src/Fieldset/index.ts
index 9d2e949e67..ee2ae05cbc 100644
--- a/packages/mui-base/src/Fieldset/index.ts
+++ b/packages/mui-base/src/Fieldset/index.ts
@@ -1,11 +1,2 @@
 export { FieldsetRoot as Root } from './Root/FieldsetRoot';
 export { FieldsetLegend as Legend } from './Legend/FieldsetLegend';
-
-export type {
-  FieldsetRootProps as RootProps,
-  FieldsetRootOwnerState as RootOwnerState,
-} from './Root/FieldsetRoot.types';
-export type {
-  FieldsetLegendProps as LegendProps,
-  FieldsetLegendOwnerState as LegendOwnerState,
-} from './Legend/FieldsetLegend.types';