diff --git a/packages/ra-ui-materialui/src/layout/AppBar.js b/packages/ra-ui-materialui/src/layout/AppBar.js
index c061d4f05ab..ed284b4f042 100644
--- a/packages/ra-ui-materialui/src/layout/AppBar.js
+++ b/packages/ra-ui-materialui/src/layout/AppBar.js
@@ -8,7 +8,6 @@ import IconButton from '@material-ui/core/IconButton';
 import Typography from '@material-ui/core/Typography';
 import { makeStyles } from '@material-ui/core/styles';
 import MenuIcon from '@material-ui/icons/Menu';
-import { useTheme } from '@material-ui/styles';
 import useMediaQuery from '@material-ui/core/useMediaQuery';
 import { toggleSidebar } from 'ra-core';
 
@@ -16,23 +15,6 @@ import LoadingIndicator from './LoadingIndicator';
 import DefaultUserMenu from './UserMenu';
 import HideOnScroll from './HideOnScroll';
 
-/**
- * Be careful using this hook. It only works because the number of
- * breakpoints in theme is static. It will break once you change the number of
- * breakpoints. See https://reactjs.org/docs/hooks-rules.html#only-call-hooks-at-the-top-level
- */
-function useWidth() {
-    const theme = useTheme();
-    const keys = [...theme.breakpoints.keys].reverse();
-    return (
-        keys.reduce((output, key) => {
-            // eslint-disable-next-line react-hooks/rules-of-hooks
-            const matches = useMediaQuery(theme.breakpoints.up(key));
-            return !output && matches ? key : output;
-        }, null) || 'xs'
-    );
-}
-
 const useStyles = makeStyles(theme => ({
     toolbar: {
         paddingRight: 24,
@@ -77,7 +59,7 @@ const AppBar = ({
     const classes = useStyles({ classes: classesOverride });
     const dispatch = useDispatch();
     const locale = useSelector(state => state.i18n.locale);
-    const width = useWidth();
+    const isXSmall = useMediaQuery(theme => theme.breakpoints.down('xs'));
 
     return (
         <HideOnScroll>
@@ -89,7 +71,7 @@ const AppBar = ({
             >
                 <Toolbar
                     disableGutters
-                    variant={width === 'xs' ? 'regular' : 'dense'}
+                    variant={isXSmall ? 'regular' : 'dense'}
                     className={classes.toolbar}
                 >
                     <IconButton