diff --git a/include/wx/cmndata.h b/include/wx/cmndata.h
index b85b01cb26..2c8c64b7c8 100644
--- a/include/wx/cmndata.h
+++ b/include/wx/cmndata.h
@@ -35,11 +35,11 @@ public:
 
     void SetChooseFull(bool flag) { chooseFull = flag; }
     bool GetChooseFull() const { return chooseFull; }
-    void SetColour(wxColour& colour) { dataColour = colour; }
+    void SetColour(const wxColour& colour) { dataColour = colour; }
     wxColour &GetColour() { return dataColour; }
 
     // Array of 16 custom colours
-    void SetCustomColour(int i, wxColour& colour);
+    void SetCustomColour(int i, const wxColour& colour);
     wxColour GetCustomColour(int i);
 
     void operator=(const wxColourData& data);
diff --git a/src/common/cmndata.cpp b/src/common/cmndata.cpp
index b0b0727f8f..eaf2321f5e 100644
--- a/src/common/cmndata.cpp
+++ b/src/common/cmndata.cpp
@@ -129,7 +129,7 @@ wxColourData::~wxColourData()
 {
 }
 
-void wxColourData::SetCustomColour(int i, wxColour& colour)
+void wxColourData::SetCustomColour(int i, const wxColour& colour)
 {
     if (i > 15 || i < 0)
         return;