diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
index 2bf704c..61336f7 100644
--- a/LayoutTests/ChangeLog
+++ b/LayoutTests/ChangeLog
@@ -1,3 +1,12 @@
+2020-04-02  Jason Lawrence  <lawrence.j@apple.com>
+
+        [ Mac wk1 Debug ] inspector/css/add-css-property.html is flaky timing out.
+        https://bugs.webkit.org/show_bug.cgi?id=209921
+
+        Unreviewed test gardening.
+
+        * platform/mac-wk1/TestExpectations:
+
 2020-04-02  Ryan Haddad  <ryanhaddad@apple.com>
 
         Unreviewed test gardening.
diff --git a/LayoutTests/platform/mac-wk1/TestExpectations b/LayoutTests/platform/mac-wk1/TestExpectations
index 00baead..a0ba1ec 100644
--- a/LayoutTests/platform/mac-wk1/TestExpectations
+++ b/LayoutTests/platform/mac-wk1/TestExpectations
@@ -950,3 +950,5 @@
 webkit.org/b/209866 [ Mojave Release ] platform/mac/media/media-source/videoplaybackquality-decompressionsession.html [ Pass Failure ]
 
 webkit.org/b/209882 [ Debug ] inspector/page/overrideSetting-ICECandidateFilteringEnabled.html [ Pass Timeout ]
+
+webkit.org/b/209921 [ Debug ] inspector/css/add-css-property.html [ Pass Timeout ]
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