diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index cba1eceb50..76ee2b3a67 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -81,7 +81,7 @@ jobs:
             containerImage:
             testRunner: Invoke-Expression
             testArguments: -excludedCategories performance GafferTest GafferVDBTest GafferUSDTest GafferSceneTest GafferDispatchTest GafferOSLTest GafferImageTest GafferUITest GafferImageUITest GafferSceneUITest GafferDispatchUITest GafferOSLUITest GafferUSDUITest GafferVDBUITest GafferDelightUITest GafferTractorTest GafferTractorUITest
-            sconsCacheMegabytes: 400
+            sconsCacheMegabytes: 800
             jobs: 4
 
     runs-on: ${{ matrix.os }}
diff --git a/Changes.md b/Changes.md
index 5445f76f39..ac88911148 100644
--- a/Changes.md
+++ b/Changes.md
@@ -21,6 +21,7 @@ Fixes
 - CodeWidget : Fixed bug that could prevent changes from being committed while the completion menu was visible.
 - Loop : Fixed handling of empty `indexVariable`. This now disables the Loop instead of creating an unnamed context variable.
 - ColorChooser : Fixed emission of `colorChangedSignal()` while the widget was in an inconsistent internal state.
+- LazyMethod : Fixed errors caused by running idle callbacks without a valid Qt Widget.
 
 API
 ---
@@ -605,11 +606,19 @@ Build
   - Removed QtNetworkAuth library.
 - USD : Updated to version 23.11.
 
-1.3.16.x (relative to 1.3.16.5)
+1.3.16.x (relative to 1.3.16.6)
 ========
 
 
 
+1.3.16.6 (relative to 1.3.16.5)
+========
+
+Fixes
+-----
+
+- LazyMethod : Fixed errors caused by running idle callbacks without a valid Qt Widget.
+
 1.3.16.5 (relative to 1.3.16.4)
 ========
 
diff --git a/python/GafferUI/LazyMethod.py b/python/GafferUI/LazyMethod.py
index 7a974e73e5..6d5458df33 100644
--- a/python/GafferUI/LazyMethod.py
+++ b/python/GafferUI/LazyMethod.py
@@ -157,7 +157,7 @@ def __playbackStateChanged( cls, playback, widgetWeakref, method ) :
 	def __idle( cls, widgetWeakref, method ) :
 
 		widget = widgetWeakref()
-		if widget is None :
+		if widget is None or not GafferUI._qtObjectIsValid( widget._qtWidget() ):
 			return
 
 		cls.__doPendingCalls( widget, method )