diff --git a/include/vcl/window.hxx b/include/vcl/window.hxx
index 5b681f2a539e..bc20cbe7550b 100644
--- a/include/vcl/window.hxx
+++ b/include/vcl/window.hxx
@@ -1192,9 +1192,11 @@ protected:
      * the preferred widget size.
      *
      * Use get_preferred_size to retrieve this value
-     * mediated via height and width requests
+     * cached and mediated via height and width requests
      */
     virtual Size GetOptimalSize() const;
+    /// clear OptimalSize cache
+    void InvalidateSizeCache();
 private:
 
     SAL_DLLPRIVATE bool                 ImplIsAccessibleCandidate() const;
diff --git a/svx/source/sidebar/PanelLayout.cxx b/svx/source/sidebar/PanelLayout.cxx
index 21fcc2d401c3..829fd3b8afad 100644
--- a/svx/source/sidebar/PanelLayout.cxx
+++ b/svx/source/sidebar/PanelLayout.cxx
@@ -51,6 +51,7 @@ void PanelLayout::queue_resize(StateChangedType /*eReason*/)
         return;
     if (!isLayoutEnabled(this))
         return;
+    InvalidateSizeCache();
     m_aPanelLayoutIdle.Start();
 }
 
diff --git a/vcl/source/window/dockwin.cxx b/vcl/source/window/dockwin.cxx
index 5a0df3cbaa46..94e32d34abf5 100644
--- a/vcl/source/window/dockwin.cxx
+++ b/vcl/source/window/dockwin.cxx
@@ -1114,9 +1114,7 @@ void DockingWindow::queue_resize(StateChangedType /*eReason*/)
         return;
     if (!isLayoutEnabled())
         return;
-    WindowImpl *pWindowImpl = mpWindowImpl->mpBorderWindow ? mpWindowImpl->mpBorderWindow->mpWindowImpl : mpWindowImpl;
-    pWindowImpl->mnOptimalWidthCache = -1;
-    pWindowImpl->mnOptimalHeightCache = -1;
+    InvalidateSizeCache();
     maLayoutIdle.Start();
 }
 
diff --git a/vcl/source/window/syswin.cxx b/vcl/source/window/syswin.cxx
index 1455c3b93e2a..c5d0522dc0e1 100644
--- a/vcl/source/window/syswin.cxx
+++ b/vcl/source/window/syswin.cxx
@@ -997,9 +997,7 @@ void SystemWindow::queue_resize(StateChangedType /*eReason*/)
         return;
     if (!isLayoutEnabled())
         return;
-    WindowImpl *pWindowImpl = mpWindowImpl->mpBorderWindow ? mpWindowImpl->mpBorderWindow->mpWindowImpl : mpWindowImpl;
-    pWindowImpl->mnOptimalWidthCache = -1;
-    pWindowImpl->mnOptimalHeightCache = -1;
+    InvalidateSizeCache();
     maLayoutIdle.Start();
 }
 
diff --git a/vcl/source/window/window2.cxx b/vcl/source/window/window2.cxx
index 691b92cd2ebc..e6672875f7c4 100644
--- a/vcl/source/window/window2.cxx
+++ b/vcl/source/window/window2.cxx
@@ -1427,16 +1427,23 @@ namespace
     }
 }
 
+void Window::InvalidateSizeCache()
+{
+    WindowImpl *pWindowImpl = mpWindowImpl->mpBorderWindow ? mpWindowImpl->mpBorderWindow->mpWindowImpl : mpWindowImpl;
+    pWindowImpl->mnOptimalWidthCache = -1;
+    pWindowImpl->mnOptimalHeightCache = -1;
+}
+
 void Window::queue_resize(StateChangedType eReason)
 {
     bool bSomeoneCares = queue_ungrouped_resize(this);
 
-    WindowImpl *pWindowImpl = mpWindowImpl->mpBorderWindow ? mpWindowImpl->mpBorderWindow->mpWindowImpl : mpWindowImpl;
     if (eReason != StateChangedType::VISIBLE)
     {
-        pWindowImpl->mnOptimalWidthCache = -1;
-        pWindowImpl->mnOptimalHeightCache = -1;
+        InvalidateSizeCache();
     }
+
+    WindowImpl *pWindowImpl = mpWindowImpl->mpBorderWindow ? mpWindowImpl->mpBorderWindow->mpWindowImpl : mpWindowImpl;
     if (pWindowImpl->m_xSizeGroup && pWindowImpl->m_xSizeGroup->get_mode() != VCL_SIZE_GROUP_NONE)
     {
         std::set<vcl::Window*> &rWindows = pWindowImpl->m_xSizeGroup->get_widgets();