diff --git a/Source/WebCore/accessibility/mac/WebAccessibilityObjectWrapperMac.mm b/Source/WebCore/accessibility/mac/WebAccessibilityObjectWrapperMac.mm
index 426333dc1f08..f2d1ff62ae7d 100644
--- a/Source/WebCore/accessibility/mac/WebAccessibilityObjectWrapperMac.mm
+++ b/Source/WebCore/accessibility/mac/WebAccessibilityObjectWrapperMac.mm
@@ -861,7 +861,7 @@ - (NSArray*)additionalAccessibilityAttributeNames
     if (AXObjectCache::isIsolatedTreeEnabled())
         [additional addObject:NSAccessibilityRelativeFrameAttribute];
 #endif
-    
+
     return additional;
 }
 
diff --git a/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.cpp b/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.cpp
index dbcf1f89114e..9b897a5b634c 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.cpp
+++ b/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.cpp
@@ -60,13 +60,6 @@ bool AccessibilityUIElement::isValid() const
 #endif
 }
 
-#if !ENABLE(ACCESSIBILITY_ISOLATED_TREE)
-bool AccessibilityUIElement::isIsolatedObject() const
-{
-    return false;
-}
-#endif
-
 // iOS specific methods
 #if !PLATFORM(IOS_FAMILY)
 JSRetainPtr<JSStringRef> AccessibilityUIElement::identifier() { return nullptr; }
diff --git a/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.h b/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.h
index 0f38df2383c3..946a0dfa0567 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.h
+++ b/Tools/WebKitTestRunner/InjectedBundle/AccessibilityUIElement.h
@@ -421,8 +421,6 @@ class AccessibilityUIElement : public JSWrappable {
     bool hasTextEntryTrait();
     RefPtr<AccessibilityUIElement> fieldsetAncestorElement();
 
-    bool isIsolatedObject() const;
-    
     bool isInsertion() const;
     bool isDeletion() const;
     bool isFirstItemInSuggestion() const;
diff --git a/Tools/WebKitTestRunner/InjectedBundle/Bindings/AccessibilityUIElement.idl b/Tools/WebKitTestRunner/InjectedBundle/Bindings/AccessibilityUIElement.idl
index ef81a3a89173..0e917abba282 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/Bindings/AccessibilityUIElement.idl
+++ b/Tools/WebKitTestRunner/InjectedBundle/Bindings/AccessibilityUIElement.idl
@@ -28,7 +28,6 @@
 ] interface AccessibilityUIElement {
     boolean isEqual(AccessibilityUIElement otherElement);
     readonly attribute DOMString domIdentifier;
-    readonly attribute boolean isIsolatedObject;
 
     // Element access.
     AccessibilityUIElement elementAtPoint(long x, long y);
diff --git a/Tools/WebKitTestRunner/InjectedBundle/mac/AccessibilityUIElementMac.mm b/Tools/WebKitTestRunner/InjectedBundle/mac/AccessibilityUIElementMac.mm
index 757e98beaa6d..62bac3a76256 100644
--- a/Tools/WebKitTestRunner/InjectedBundle/mac/AccessibilityUIElementMac.mm
+++ b/Tools/WebKitTestRunner/InjectedBundle/mac/AccessibilityUIElementMac.mm
@@ -96,7 +96,6 @@
 typedef void (*AXPostedNotificationCallback)(id element, NSString* notification, void* context);
 
 @interface NSObject (WebKitAccessibilityAdditions)
-- (BOOL)isIsolatedObject;
 - (BOOL)accessibilityReplaceRange:(NSRange)range withText:(NSString *)string;
 - (BOOL)accessibilityInsertText:(NSString *)text;
 - (NSArray *)accessibilityArrayAttributeValues:(NSString *)attribute index:(NSUInteger)index maxCount:(NSUInteger)maxCount;
@@ -135,21 +134,6 @@ - (void)_accessibilitySetValue:(id)value forAttribute:(NSString*)attributeName;
     return platformUIElement() == otherElement->platformUIElement();
 }
 
-#if ENABLE(ACCESSIBILITY_ISOLATED_TREE)
-bool AccessibilityUIElement::isIsolatedObject() const
-{
-    BOOL value;
-
-    BEGIN_AX_OBJC_EXCEPTIONS
-    s_controller->executeOnAXThreadAndWait([this, &value] {
-        value = [m_element isIsolatedObject];
-    });
-    END_AX_OBJC_EXCEPTIONS
-
-    return value;
-}
-#endif
-
 RetainPtr<NSArray> supportedAttributes(id element)
 {
     RetainPtr<NSArray> attributes;