diff --git a/resources/skins.vector.js/sidebarPersistence.js b/resources/skins.vector.js/sidebarPersistence.js
index 8014d017..4f637c0f 100644
--- a/resources/skins.vector.js/sidebarPersistence.js
+++ b/resources/skins.vector.js/sidebarPersistence.js
@@ -11,19 +11,36 @@ var /** @type {MwApi} */api,
 	SIDEBAR_CHECKBOX_ID = 'mw-sidebar-checkbox',
 	SIDEBAR_PREFERENCE_NAME = 'VectorSidebarVisible';
 
+/**
+ * Checks if persistent is enabled at current time.
+ * When a user is using a browser with a screen resolution of < 1000 it is assumed
+ * that it is preferred that the sidebar remains closed across page views, as otherwise
+ * it gets in the way of reading. More context at T316191.
+ *
+ * @return {boolean}
+ */
+function isPersistentEnabled() {
+	return window.innerWidth >= 1000;
+}
+
 /**
  * Execute a debounced API request to save the sidebar user preference.
  * The request is meant to fire 1000 milliseconds after the last click on
  * the sidebar button.
  *
  * @param {HTMLInputElement} checkbox
+ * @param {number} timeout duration
+ * @param {boolean} shouldTriggerResize whether a resize event is needed.
  * @return {any}
  */
-function saveSidebarState( checkbox ) {
+function saveSidebarState( checkbox, timeout, shouldTriggerResize ) {
 	return debounce( function () {
 		api = api || new mw.Api();
 		api.saveOption( SIDEBAR_PREFERENCE_NAME, checkbox.checked ? 1 : 0 );
 
+		if ( !shouldTriggerResize ) {
+			return;
+		}
 		// Trigger a resize event so other parts of the page can adapt:
 		var event;
 		if ( typeof Event === 'function' ) {
@@ -34,7 +51,7 @@ function saveSidebarState( checkbox ) {
 			event.initUIEvent( 'resize', true, false, window, 0 );
 		}
 		window.dispatchEvent( event );
-	}, 1000 );
+	}, timeout );
 }
 
 /**
@@ -46,17 +63,79 @@ function saveSidebarState( checkbox ) {
  */
 function bindSidebarClickEvent( checkbox, button ) {
 	if ( checkbox instanceof HTMLInputElement && button ) {
-		checkbox.addEventListener( 'input', saveSidebarState( checkbox ) );
+		var handler = saveSidebarState( checkbox, 1000, true );
+		checkbox.addEventListener( 'input', function () {
+			if ( isPersistentEnabled() ) {
+				handler();
+			}
+		} );
+	}
+}
+
+var /** @type {boolean} */ wasCollapsedDuringResize = false;
+
+/**
+ * Collapses the sidebar if screen resolution too small.
+ *
+ * @param {HTMLInputElement} checkbox
+ */
+function collapseSidebar( checkbox ) {
+	if ( checkbox.checked ) {
+		wasCollapsedDuringResize = true;
+		checkbox.checked = false;
+		saveSidebarState( checkbox, 0, false )();
+	}
+}
+
+/**
+ * Expands the sidebar when the window is resized if it was previously collapsed.
+ *
+ * @param {HTMLInputElement} checkbox
+ */
+function expandSidebar( checkbox ) {
+	if ( wasCollapsedDuringResize && !checkbox.checked ) {
+		wasCollapsedDuringResize = false;
+		checkbox.checked = true;
+		saveSidebarState( checkbox, 0, false )();
 	}
 }
 
 function init() {
-	var checkbox = window.document.getElementById( SIDEBAR_CHECKBOX_ID ),
+	var checkbox = /** @type {HTMLInputElement|null} */ (
+			window.document.getElementById( SIDEBAR_CHECKBOX_ID )
+		),
 		button = window.document.getElementById( SIDEBAR_BUTTON_ID );
 
 	if ( mw.config.get( 'wgUserName' ) && !mw.config.get( 'wgVectorDisableSidebarPersistence' ) ) {
 		bindSidebarClickEvent( checkbox, button );
 	}
+
+	// If the user has resized their window, an open sidebar will be taking up lots of space
+	// so we should disable it.
+	// When this happens the user must expand it again manually, to avoid conflicts with multiple
+	// open windows (for example when an editor is viewing 2 articles side by side).
+	if ( checkbox ) {
+		var mediaQuery = window.matchMedia( '(max-width: 1000px)' );
+		var onMediaQueryChangeCollapse = function ( /** @type {MediaQueryListEvent} */ event ) {
+			if ( event.matches ) {
+				// @ts-ignore we checked it already.
+				collapseSidebar( checkbox );
+			} else {
+				// @ts-ignore we checked it already.
+				expandSidebar( checkbox );
+			}
+		};
+		if ( mediaQuery.matches ) {
+			collapseSidebar( checkbox );
+		}
+		if ( mediaQuery.addEventListener ) {
+			mediaQuery.addEventListener( 'change', onMediaQueryChangeCollapse );
+		} else {
+			//  Before Safari 14, MediaQueryList is based on EventTarget,
+			// so you must use addListener() and removeListener() to observe media query lists.
+			mediaQuery.addListener( onMediaQueryChangeCollapse );
+		}
+	}
 }
 
 module.exports = {