diff --git a/include/wx/cmdproc.h b/include/wx/cmdproc.h
index 6072e7fda0..4fa3e34c19 100644
--- a/include/wx/cmdproc.h
+++ b/include/wx/cmdproc.h
@@ -97,10 +97,7 @@ public:
     virtual void ClearCommands();
 
     // Has the current project been changed?
-    virtual bool IsDirty() const
-    {
-        return m_currentCommand && (m_lastSavedCommand != m_currentCommand);
-    }
+    virtual bool IsDirty() const;
 
     // Mark the current command as the one where the last save took place
     void MarkAsSaved()
diff --git a/src/common/cmdproc.cpp b/src/common/cmdproc.cpp
index 7de08c2790..ed7efb3e3f 100644
--- a/src/common/cmdproc.cpp
+++ b/src/common/cmdproc.cpp
@@ -328,4 +328,14 @@ void wxCommandProcessor::ClearCommands()
     m_lastSavedCommand = wxList::compatibility_iterator();
 }
 
+bool wxCommandProcessor::IsDirty() const
+{
+    if ( !m_currentCommand )
+        return false;
+
+    if ( !m_lastSavedCommand )
+        return true;
+
+    return m_lastSavedCommand != m_currentCommand;
+}