diff --git a/include/wx/generic/private/textmeasure.h b/include/wx/generic/private/textmeasure.h
index 5d44f35350..c3ab30da70 100644
--- a/include/wx/generic/private/textmeasure.h
+++ b/include/wx/generic/private/textmeasure.h
@@ -18,9 +18,9 @@
 class wxTextMeasure : public wxTextMeasureBase
 {
 public:
-    wxTextMeasure(const wxDC *dc, const wxFont *font)
+    wxEXPLICIT wxTextMeasure(const wxDC *dc, const wxFont *font = NULL)
         : wxTextMeasureBase(dc, font) {}
-    wxTextMeasure(const wxWindow *win, const wxFont *font)
+    wxEXPLICIT wxTextMeasure(const wxWindow *win, const wxFont *font = NULL)
         : wxTextMeasureBase(win, font) {}
 
 protected:
diff --git a/include/wx/gtk/private/textmeasure.h b/include/wx/gtk/private/textmeasure.h
index 5027be7b35..d32466f287 100644
--- a/include/wx/gtk/private/textmeasure.h
+++ b/include/wx/gtk/private/textmeasure.h
@@ -20,13 +20,13 @@ class WXDLLIMPEXP_FWD_CORE wxWindowDCImpl;
 class wxTextMeasure : public wxTextMeasureBase
 {
 public:
-    wxTextMeasure(const wxDC *dc, const wxFont *font)
+    wxEXPLICIT wxTextMeasure(const wxDC *dc, const wxFont *font = NULL)
         : wxTextMeasureBase(dc, font)
     {
         Init();
     }
 
-    wxTextMeasure(const wxWindow *win, const wxFont *font)
+    wxEXPLICIT wxTextMeasure(const wxWindow *win, const wxFont *font = NULL)
         : wxTextMeasureBase(win, font)
     {
         Init();
diff --git a/include/wx/msw/private/textmeasure.h b/include/wx/msw/private/textmeasure.h
index a52deb59a1..e317510ffe 100644
--- a/include/wx/msw/private/textmeasure.h
+++ b/include/wx/msw/private/textmeasure.h
@@ -20,12 +20,13 @@
 class wxTextMeasure : public wxTextMeasureBase
 {
 public:
-    wxTextMeasure(const wxDC *dc, const wxFont *font)
+    wxEXPLICIT wxTextMeasure(const wxDC *dc, const wxFont *font = NULL)
         : wxTextMeasureBase(dc, font)
     {
         Init();
     }
-    wxTextMeasure(const wxWindow *win, const wxFont *font)
+
+    wxEXPLICIT wxTextMeasure(const wxWindow *win, const wxFont *font = NULL)
         : wxTextMeasureBase(win, font)
     {
         Init();