diff --git a/LayoutTests/accessibility/mac/expanded-notification-expected.txt b/LayoutTests/accessibility/mac/expanded-notification-expected.txt
index e3f21bd5c6f94..d8faa3f4a4f22 100644
--- a/LayoutTests/accessibility/mac/expanded-notification-expected.txt
+++ b/LayoutTests/accessibility/mac/expanded-notification-expected.txt
@@ -1,11 +1,19 @@
-This tests that aria-expanded changes will send notifications.
+This tests that expanded notifications will be sent when the appropriate changes occur.
 Initial expanded status: false
 Received notification: AXExpandedChanged
 Expanded status: true
 Received notification: AXExpandedChanged
 Expanded status: false
+PASS: accessibilityController.accessibleElementById('show-popover-btn').isExpanded === false
+PASS: accessibilityController.accessibleElementById('hide-popover-btn').isExpanded === false
+Received notification: AXExpandedChanged
+Expanded status: true
+PASS: accessibilityController.accessibleElementById('hide-popover-btn').isExpanded === true
+Received notification: AXExpandedChanged
+Expanded status: false
+PASS: accessibilityController.accessibleElementById('show-popover-btn').isExpanded === false
 
 PASS successfullyParsed is true
 
 TEST COMPLETE
-
+Show popover Hide popover
diff --git a/LayoutTests/accessibility/mac/expanded-notification.html b/LayoutTests/accessibility/mac/expanded-notification.html
index e1b1853a41f29..6b8e015352d73 100644
--- a/LayoutTests/accessibility/mac/expanded-notification.html
+++ b/LayoutTests/accessibility/mac/expanded-notification.html
@@ -8,46 +8,56 @@
 
 <button id="button" aria-expanded="false">
 
+<button id="show-popover-btn" popovertarget="mypopover" popovertargetaction="show">Show popover</button>
+<button id="hide-popover-btn" popovertarget="mypopover" popovertargetaction="hide">Hide popover</button>
+<div id="mypopover" popover>Popover content</div>
+
 <script>
-    let output = "This tests that aria-expanded changes will send notifications.\n";
+let output = "This tests that expanded notifications will be sent when the appropriate changes occur.\n";
 
-    let notificationCount = 0;
-    function notificationCallback(element, notification) {
-        if (notification == "AXExpandedChanged") {
-            notificationCount++;
+let notificationCount = 0;
+function notificationCallback(element, notification) {
+    if (notification == "AXExpandedChanged") {
+        notificationCount++;
 
-            output += `Received notification: ${notification}\n`;
-            output += `Expanded status: ${element.isExpanded}\n`;
-        }
+        output += `Received notification: ${notification}\n`;
+        output += `Expanded status: ${element.isExpanded}\n`;
     }
+}
 
-    if (window.accessibilityController) {
-        window.jsTestIsAsync = true;
+if (window.accessibilityController) {
+    window.jsTestIsAsync = true;
 
-        accessibilityController.addNotificationListener(notificationCallback);
-        let button = accessibilityController.accessibleElementById("button");
-        output += `Initial expanded status: ${button.isExpanded}\n`;
+    accessibilityController.addNotificationListener(notificationCallback);
+    let button = accessibilityController.accessibleElementById("button");
+    output += `Initial expanded status: ${button.isExpanded}\n`;
 
-        document.getElementById("button").setAttribute("aria-expanded", "true");
-        setTimeout(async () => {
-            await waitFor(() => {
-                return button.isExpanded;
-            });
+    document.getElementById("button").setAttribute("aria-expanded", "true");
+    setTimeout(async () => {
+        await waitFor(() => button.isExpanded);
 
-            document.getElementById("button").setAttribute("aria-expanded", "false");
-            await waitFor(() => {
-                return !button.isExpanded;
-            });
+        document.getElementById("button").setAttribute("aria-expanded", "false");
+        await waitFor(() => !button.isExpanded);
+        await waitFor(() => notificationCount == 2);
 
-            await waitFor(() => {
-                return notificationCount == 2;
-            });
+        // Now test popover.
+        output += expect("accessibilityController.accessibleElementById('show-popover-btn').isExpanded", "false");
+        output += expect("accessibilityController.accessibleElementById('hide-popover-btn').isExpanded", "false");
 
-            debug(output);
-            accessibilityController.removeNotificationListener();
-            finishJSTest();
-        }, 0);
-    }
+        document.getElementById("show-popover-btn").click();
+        await waitFor(() => notificationCount == 3);
+        // We expanded the popover via #show-popover-btn, but #hide-popover-btn (which is also linked to the popover) should be considered expanded now as well.
+        output += await expectAsync("accessibilityController.accessibleElementById('hide-popover-btn').isExpanded", "true");
+
+        document.getElementById("hide-popover-btn").click();
+        await waitFor(() => notificationCount == 4);
+        output += await expectAsync("accessibilityController.accessibleElementById('show-popover-btn').isExpanded", "false");
+
+        debug(output);
+        accessibilityController.removeNotificationListener();
+        finishJSTest();
+    }, 0);
+}
 </script>
 </body>
 </html>
diff --git a/Source/WebCore/accessibility/AXObjectCache.cpp b/Source/WebCore/accessibility/AXObjectCache.cpp
index a0fa72b5496fc..0e31e4adc5281 100644
--- a/Source/WebCore/accessibility/AXObjectCache.cpp
+++ b/Source/WebCore/accessibility/AXObjectCache.cpp
@@ -1472,6 +1472,11 @@ void AXObjectCache::onFocusChange(Node* oldNode, Node* newNode)
         handleFocusedUIElementChanged(oldNode, newNode);
 }
 
+void AXObjectCache::onPopoverTargetToggle(const HTMLFormControlElement& popoverInvokerElement)
+{
+    postNotification(get(const_cast<HTMLFormControlElement*>(&popoverInvokerElement)), &document(), AXExpandedChanged);
+}
+
 void AXObjectCache::deferMenuListValueChange(Element* element)
 {
     if (!element)
diff --git a/Source/WebCore/accessibility/AXObjectCache.h b/Source/WebCore/accessibility/AXObjectCache.h
index 9b2caf9e087df..b3afd42056e87 100644
--- a/Source/WebCore/accessibility/AXObjectCache.h
+++ b/Source/WebCore/accessibility/AXObjectCache.h
@@ -182,6 +182,7 @@ class AXObjectCache : public CanMakeWeakPtr<AXObjectCache>, public CanMakeChecke
     void childrenChanged(RenderObject*, RenderObject* newChild = nullptr);
     void childrenChanged(AccessibilityObject*);
     void onFocusChange(Node* oldFocusedNode, Node* newFocusedNode);
+    void onPopoverTargetToggle(const HTMLFormControlElement&);
     void onScrollbarFrameRectChange(const Scrollbar&);
     void onSelectedChanged(Node*);
     void onTextSecurityChanged(HTMLInputElement&);
diff --git a/Source/WebCore/accessibility/AccessibilityNodeObject.cpp b/Source/WebCore/accessibility/AccessibilityNodeObject.cpp
index a757a63957520..49cf28c3b8453 100644
--- a/Source/WebCore/accessibility/AccessibilityNodeObject.cpp
+++ b/Source/WebCore/accessibility/AccessibilityNodeObject.cpp
@@ -1107,6 +1107,12 @@ Element* AccessibilityNodeObject::anchorElement() const
     return nullptr;
 }
 
+Element* AccessibilityNodeObject::popoverTargetElement() const
+{
+    WeakPtr formControlElement = dynamicDowncast<HTMLFormControlElement>(node());
+    return formControlElement ? formControlElement->popoverTargetElement() : nullptr;
+}
+
 AccessibilityObject* AccessibilityNodeObject::internalLinkElement() const
 {
     // We don't currently support ARIA links as internal link elements, so exit early if anchorElement() is not a native HTMLAnchorElement.
diff --git a/Source/WebCore/accessibility/AccessibilityNodeObject.h b/Source/WebCore/accessibility/AccessibilityNodeObject.h
index 713e61e45584a..ce0ea4038ef7a 100644
--- a/Source/WebCore/accessibility/AccessibilityNodeObject.h
+++ b/Source/WebCore/accessibility/AccessibilityNodeObject.h
@@ -121,6 +121,7 @@ class AccessibilityNodeObject : public AccessibilityObject {
     Element* actionElement() const override;
     Element* mouseButtonListener(MouseButtonListenerResultFilter = ExcludeBodyElement) const;
     Element* anchorElement() const override;
+    Element* popoverTargetElement() const final;
     AccessibilityObject* internalLinkElement() const;
     void addRadioButtonGroupMembers(AccessibilityChildrenVector& linkedUIElements) const;
     void addRadioButtonGroupChildren(AXCoreObject&, AccessibilityChildrenVector&) const;
diff --git a/Source/WebCore/accessibility/AccessibilityObject.cpp b/Source/WebCore/accessibility/AccessibilityObject.cpp
index 59e684f27a907..44788750036cf 100644
--- a/Source/WebCore/accessibility/AccessibilityObject.cpp
+++ b/Source/WebCore/accessibility/AccessibilityObject.cpp
@@ -3269,6 +3269,10 @@ bool AccessibilityObject::supportsPressed() const
     
 bool AccessibilityObject::supportsExpanded() const
 {
+    // If this object can toggle an HTML popover, it supports the reporting of its expanded state (which is based on the expanded / collapsed state of that popover).
+    if (popoverTargetElement())
+        return true;
+
     switch (roleValue()) {
     case AccessibilityRole::Button:
     case AccessibilityRole::CheckBox:
@@ -3322,8 +3326,11 @@ bool AccessibilityObject::isExpanded() const
             return parent->isExpanded();
     }
 
-    if (supportsExpanded())
+    if (supportsExpanded()) {
+        if (WeakPtr popoverTargetElement = this->popoverTargetElement())
+            return popoverTargetElement->isPopoverShowing();
         return equalLettersIgnoringASCIICase(getAttribute(aria_expandedAttr), "true"_s);
+    }
 
     return false;  
 }
diff --git a/Source/WebCore/accessibility/AccessibilityObject.h b/Source/WebCore/accessibility/AccessibilityObject.h
index ca3a33c47d53a..bda2ccd281336 100644
--- a/Source/WebCore/accessibility/AccessibilityObject.h
+++ b/Source/WebCore/accessibility/AccessibilityObject.h
@@ -423,6 +423,7 @@ class AccessibilityObject : public AXCoreObject, public CanMakeWeakPtr<Accessibi
     static AccessibilityObject* anchorElementForNode(Node*);
     static AccessibilityObject* headingElementForNode(Node*);
     virtual Element* anchorElement() const { return nullptr; }
+    virtual Element* popoverTargetElement() const { return nullptr; }
     bool supportsPressAction() const override;
     Element* actionElement() const override { return nullptr; }
     virtual LayoutRect boundingBoxRect() const { return { }; }
diff --git a/Source/WebCore/html/HTMLFormControlElement.cpp b/Source/WebCore/html/HTMLFormControlElement.cpp
index 59b3c71b1a6fa..f91620f9f7517 100644
--- a/Source/WebCore/html/HTMLFormControlElement.cpp
+++ b/Source/WebCore/html/HTMLFormControlElement.cpp
@@ -395,11 +395,20 @@ void HTMLFormControlElement::handlePopoverTargetAction() const
 
     auto action = popoverTargetAction();
     bool canHide = action == hideAtom() || action == toggleAtom();
+    bool shouldHide = canHide && target->popoverData()->visibilityState() == PopoverVisibilityState::Showing;
     bool canShow = action == showAtom() || action == toggleAtom();
-    if (canHide && target->popoverData()->visibilityState() == PopoverVisibilityState::Showing)
+    bool shouldShow = canShow && target->popoverData()->visibilityState() == PopoverVisibilityState::Hidden;
+
+    if (shouldHide)
         target->hidePopover();
-    else if (canShow && target->popoverData()->visibilityState() == PopoverVisibilityState::Hidden)
+    else if (shouldShow)
         target->showPopover(this);
+
+    if (shouldHide || shouldShow) {
+        // Accessibility needs to know that the invoker (this) toggled popover visibility state.
+        if (auto* cache = document().existingAXObjectCache())
+            cache->onPopoverTargetToggle(*this);
+    }
 }
 
 // FIXME: We should remove the quirk once <rdar://problem/47334655> is fixed.