diff --git a/include/wx/list.h b/include/wx/list.h
index 8499b8a94f..7d1f0ebc1a 100644
--- a/include/wx/list.h
+++ b/include/wx/list.h
@@ -166,7 +166,11 @@ private:
             const compatibility_iterator* operator->() const { return this; } \
                                                                               \
             bool operator==(const compatibility_iterator& i) const            \
-                { return (m_list == i.m_list) && (m_iter == i.m_iter); }      \
+            {                                                                 \
+                wxASSERT_MSG( m_list && i.m_list,                             \
+                              _T("comparing invalid iterators is illegal") ); \
+                return (m_list == i.m_list) && (m_iter == i.m_iter);          \
+            }                                                                 \
             bool operator!=(const compatibility_iterator& i) const            \
                 { return !( operator==( i ) ); }                              \
             operator bool() const                                             \