diff --git a/include/wx/window.h b/include/wx/window.h
index 1b88bc156c..7a20ca1615 100644
--- a/include/wx/window.h
+++ b/include/wx/window.h
@@ -317,7 +317,7 @@ public:
 
         // reset the cached best size value so it will be recalculated the
         // next time it is needed.
-    void InvalidateBestSize() { m_bestSizeCache = wxDefaultSize; }
+    void InvalidateBestSize();
     void CacheBestSize(const wxSize& size) const
         { wxConstCast(this, wxWindowBase)->m_bestSizeCache = size; }
 
diff --git a/src/common/wincmn.cpp b/src/common/wincmn.cpp
index 784b618111..c15d4f4da9 100644
--- a/src/common/wincmn.cpp
+++ b/src/common/wincmn.cpp
@@ -530,6 +530,16 @@ static bool wxHasRealChildren(const wxWindowBase* win)
     return (realChildCount > 0);
 }
 #endif
+    
+void wxWindowBase::InvalidateBestSize()
+{
+    m_bestSizeCache = wxDefaultSize;
+
+    // parent's best size calculation may depend on its children's
+    // best sizes, so let's invalidate it as well to be safe:
+    if (m_parent)
+        m_parent->InvalidateBestSize();
+}
 
 // return the size best suited for the current window
 wxSize wxWindowBase::DoGetBestSize() const