diff --git a/packages/mui-private-theming/src/ThemeProvider/ThemeProvider.js b/packages/mui-private-theming/src/ThemeProvider/ThemeProvider.js
index 78eee6f0ca023c..37930eaabc72e5 100644
--- a/packages/mui-private-theming/src/ThemeProvider/ThemeProvider.js
+++ b/packages/mui-private-theming/src/ThemeProvider/ThemeProvider.js
@@ -52,7 +52,8 @@ function ThemeProvider(props) {
   }
 
   const theme = React.useMemo(() => {
-    const output = outerTheme === null ? localTheme : mergeOuterLocalTheme(outerTheme, localTheme);
+    const output =
+      outerTheme === null ? { ...localTheme } : mergeOuterLocalTheme(outerTheme, localTheme);
 
     if (output != null) {
       output[nested] = outerTheme !== null;
diff --git a/packages/mui-private-theming/src/useTheme/useTheme.js b/packages/mui-private-theming/src/useTheme/useTheme.js
index f1dffd12ccfaa1..43c5f29ed82888 100644
--- a/packages/mui-private-theming/src/useTheme/useTheme.js
+++ b/packages/mui-private-theming/src/useTheme/useTheme.js
@@ -5,7 +5,8 @@ export default function useTheme() {
   const theme = React.useContext(ThemeContext);
 
   if (process.env.NODE_ENV !== 'production') {
-    // eslint-disable-next-line react-hooks/rules-of-hooks
+    // TODO: uncomment once we enable eslint-plugin-react-compiler eslint-disable-next-line react-compiler/react-compiler
+    // eslint-disable-next-line react-hooks/rules-of-hooks -- It's not required to run React.useDebugValue in production
     React.useDebugValue(theme);
   }