diff --git a/include/wx/gtk/bitmap.h b/include/wx/gtk/bitmap.h
index 2c8c37975a..3dccd3668f 100644
--- a/include/wx/gtk/bitmap.h
+++ b/include/wx/gtk/bitmap.h
@@ -137,6 +137,9 @@ public:
     void *GetRawData(wxPixelDataBase& data, int bpp);
     void UngetRawData(wxPixelDataBase& data);
 
+    bool HasAlpha() const { return true; }
+    void UseAlpha() { }
+
 protected:
     bool CreateFromXpm(const char **bits);
     bool CreateFromImage(const wxImage& image, int depth);
diff --git a/include/wx/gtk1/bitmap.h b/include/wx/gtk1/bitmap.h
index 2c8c37975a..3dccd3668f 100644
--- a/include/wx/gtk1/bitmap.h
+++ b/include/wx/gtk1/bitmap.h
@@ -137,6 +137,9 @@ public:
     void *GetRawData(wxPixelDataBase& data, int bpp);
     void UngetRawData(wxPixelDataBase& data);
 
+    bool HasAlpha() const { return true; }
+    void UseAlpha() { }
+
 protected:
     bool CreateFromXpm(const char **bits);
     bool CreateFromImage(const wxImage& image, int depth);