[core] Guard against bad Symbol polyfills (#17336)

mui · Sep 6, 2019 · 310409e · 310409e
1 parent f8076d6
commit 310409e
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/packages/material-ui-styles/src/ThemeProvider/nested.js b/packages/material-ui-styles/src/ThemeProvider/nested.js
@@ -1,3 +1,3 @@
-const hasSymbol = typeof Symbol === 'function';
+const hasSymbol = typeof Symbol === 'function' && Symbol.for;
 
 export default (hasSymbol ? Symbol.for('mui.nested') : '__THEME_NESTED__');