diff --git a/WebCore/ChangeLog b/WebCore/ChangeLog
index 726a3248e54bb0e17bb3d5319257bc5e0df66aa0..2c63d3fda8a337cd89a7a3ea613e4f1e4a35c7ff 100644
--- a/WebCore/ChangeLog
+++ b/WebCore/ChangeLog
@@ -1,3 +1,19 @@
+2009-09-18  Alexey Proskuryakov  <ap@apple.com>
+
+        Reviewed by Darin Adler.
+
+        https://bugs.webkit.org/show_bug.cgi?id=29510
+        Active DOM objects should be suspended while a modal dialog is displayed
+
+        * manual-tests/js-timers-beneath-modal-dialog.html: Added a test for JS timers.
+
+        * page/PageGroupLoadDeferrer.cpp:
+        (WebCore::PageGroupLoadDeferrer::PageGroupLoadDeferrer):
+        (WebCore::PageGroupLoadDeferrer::~PageGroupLoadDeferrer):
+        Match other platforms, and make Mac also suspend active DOM objects. Since a page that
+        currently displays a modal dialog cannot go into page cache, there is no danger of suspending
+        an object twice.        
+
 2009-09-18  Csaba Osztrogonac  <oszi@inf.u-szeged.hu>
 
         Reviewed by Eric Seidel.
diff --git a/WebCore/manual-tests/js-timers-beneath-modal-dialog.html b/WebCore/manual-tests/js-timers-beneath-modal-dialog.html
new file mode 100644
index 0000000000000000000000000000000000000000..6d5f2c7edf81aba675f2cd631b82df52c1e5e5e8
--- /dev/null
+++ b/WebCore/manual-tests/js-timers-beneath-modal-dialog.html
@@ -0,0 +1,19 @@
+<p>JS timers should be paused while a modal dialog (or alert) is displayed.</p>
+<p>Please disable popup blocker for this test.</p>
+<div>0</div>
+<script>
+function f()
+{
+    var d = document.getElementsByTagName("div")[0];
+    d.innerHTML = parseInt(d.innerHTML) + 1;
+}
+
+var timerId = setInterval(f, 100);
+
+alert("Numbers in main window should not increase while this alert is displayed");
+showModalDialog("data:text/html,<p>Numbers in main window should not increase while this modal dialog is displayed</p>");
+document.getElementsByTagName("div")[0].innerHTML = "DONE";
+
+clearInterval(timerId);
+
+</script>
diff --git a/WebCore/page/PageGroupLoadDeferrer.cpp b/WebCore/page/PageGroupLoadDeferrer.cpp
index f274de3e88910508a794205959dd88a0c1a1b9b8..122658b50f62574efbf6cd8f2ddb59339d679bb4 100644
--- a/WebCore/page/PageGroupLoadDeferrer.cpp
+++ b/WebCore/page/PageGroupLoadDeferrer.cpp
@@ -41,10 +41,10 @@ PageGroupLoadDeferrer::PageGroupLoadDeferrer(Page* page, bool deferSelf)
             if (!otherPage->defersLoading())
                 m_deferredFrames.append(otherPage->mainFrame());
 
-#if !PLATFORM(MAC)
+            // This code is not logically part of load deferring, but we do not want JS code executed beneath modal
+            // windows or sheets, which is exactly when PageGroupLoadDeferrer is used.
             for (Frame* frame = otherPage->mainFrame(); frame; frame = frame->tree()->traverseNext())
                 frame->document()->suspendActiveDOMObjects();
-#endif
         }
     }
 
@@ -60,10 +60,8 @@ PageGroupLoadDeferrer::~PageGroupLoadDeferrer()
         if (Page* page = m_deferredFrames[i]->page()) {
             page->setDefersLoading(false);
 
-#if !PLATFORM(MAC)
             for (Frame* frame = page->mainFrame(); frame; frame = frame->tree()->traverseNext())
                 frame->document()->resumeActiveDOMObjects();
-#endif
         }
     }
 }