diff --git a/include/wx/window.h b/include/wx/window.h
index 9ae3e47848..06d52fc835 100644
--- a/include/wx/window.h
+++ b/include/wx/window.h
@@ -374,12 +374,8 @@ public:
         // get the size best suited for the window (in fact, minimal
         // acceptable size using which it will still look "nice" in
         // most situations)
-    wxSize GetBestSize() const
-    {
-        if (m_bestSizeCache.IsFullySpecified())
-            return m_bestSizeCache;
-        return DoGetBestSize();
-    }
+    wxSize GetBestSize() const;
+    
     void GetBestSize(int *w, int *h) const
     {
         wxSize s = GetBestSize();
diff --git a/src/common/wincmn.cpp b/src/common/wincmn.cpp
index 5bb116f600..96e14509b3 100644
--- a/src/common/wincmn.cpp
+++ b/src/common/wincmn.cpp
@@ -47,6 +47,8 @@
     #include "wx/menu.h"
 #endif //WX_PRECOMP
 
+#include "wx/collpane.h"
+
 #if wxUSE_DRAG_AND_DROP
     #include "wx/dnd.h"
 #endif // wxUSE_DRAG_AND_DROP
@@ -720,6 +722,13 @@ wxSize wxWindowBase::GetEffectiveMinSize() const
     return min;
 }
 
+wxSize wxWindowBase::GetBestSize() const
+{
+    if ((!m_windowSizer) && (m_bestSizeCache.IsFullySpecified()))
+        return m_bestSizeCache;
+        
+    return DoGetBestSize();
+}
 
 void wxWindowBase::SetMinSize(const wxSize& minSize)
 {