diff --git a/packages/material-ui/src/Paper/Paper.test.js b/packages/material-ui/src/Paper/Paper.test.js
index 9234ba53101062..661a16b859b531 100644
--- a/packages/material-ui/src/Paper/Paper.test.js
+++ b/packages/material-ui/src/Paper/Paper.test.js
@@ -72,9 +72,6 @@ describe('<Paper />', () => {
 
   it('allows custom elevations via theme.shadows', () => {
     const theme = createMuiTheme();
-    // Theme.shadows holds a reference to `@material-ui/core/styles#shadows`
-    // Mutating it causes side effects in other tests
-    theme.shadows = theme.shadows.slice();
     theme.shadows.push('20px 20px');
     const { getByTestId } = render(
       <ThemeProvider theme={theme}>
diff --git a/packages/material-ui/src/styles/createMuiTheme.js b/packages/material-ui/src/styles/createMuiTheme.js
index 065efc098bb4ef..7f09210e54f003 100644
--- a/packages/material-ui/src/styles/createMuiTheme.js
+++ b/packages/material-ui/src/styles/createMuiTheme.js
@@ -30,12 +30,13 @@ function createMuiTheme(options = {}, ...args) {
       mixins: createMixins(breakpoints, spacing, mixinsInput),
       components: {}, // Inject component definitions
       palette,
-      shadows,
+      // Don't use [...shadows] until you've verified its transpiled code is not invoking the iterator protocol.
+      shadows: shadows.slice(),
       typography: createTypography(palette, typographyInput),
       spacing,
-      shape,
+      shape: { ...shape },
       transitions: { duration, easing, create, getAutoHeightDuration },
-      zIndex,
+      zIndex: { ...zIndex },
     },
     other,
   );