diff --git a/include/wx/x11/app.h b/include/wx/x11/app.h
index 0a689ed00f..f770198fc6 100644
--- a/include/wx/x11/app.h
+++ b/include/wx/x11/app.h
@@ -74,7 +74,9 @@ public:
     // Processes an X event.
     virtual bool ProcessXEvent(WXEvent* event);
     
+#ifdef __WXDEBUG__
     virtual void OnAssert(const wxChar *file, int line, const wxChar *msg);
+#endif // __WXDEBUG__
     
 protected:
     bool                  m_showOnInit;
diff --git a/src/x11/app.cpp b/src/x11/app.cpp
index 46eeb9379a..a1eb5192b5 100644
--- a/src/x11/app.cpp
+++ b/src/x11/app.cpp
@@ -1219,6 +1219,8 @@ bool wxApp::Yield(bool onlyIfNeeded)
     return TRUE;
 }
 
+#ifdef __WXDEBUG__
+
 void wxApp::OnAssert(const wxChar *file, int line, const wxChar *msg)
 {
     // While the GUI isn't working that well, just print out the
@@ -1232,3 +1234,5 @@ void wxApp::OnAssert(const wxChar *file, int line, const wxChar *msg)
 #endif
 }
 
+#endif // __WXDEBUG__
+