diff --git a/include/wx/gtk/dc.h b/include/wx/gtk/dc.h
index 3e3b600f68..3c8619cb8a 100644
--- a/include/wx/gtk/dc.h
+++ b/include/wx/gtk/dc.h
@@ -35,10 +35,10 @@ public:
     virtual wxSize GetPPI() const wxOVERRIDE;
 
 protected:
-    int m_width, m_height;
+    // Set m_width and m_height from the given (valid) GdkWindow.
+    void InitSize(GdkWindow* window);
 
-private:
-    bool TryGetWindowSize(wxSize& size, wxSize& sizeMM) const;
+    int m_width, m_height;
 
     wxDECLARE_NO_COPY_CLASS(wxGTKCairoDCImpl);
 };
diff --git a/src/gtk/dc.cpp b/src/gtk/dc.cpp
index ccd61f9b02..79c90e20d2 100644
--- a/src/gtk/dc.cpp
+++ b/src/gtk/dc.cpp
@@ -55,6 +55,12 @@ wxGTKCairoDCImpl::wxGTKCairoDCImpl(wxDC* owner, wxWindow* window)
     m_contentScaleFactor = window->GetContentScaleFactor();
 }
 
+void wxGTKCairoDCImpl::InitSize(GdkWindow* window)
+{
+    m_width = gdk_window_get_width(window);
+    m_height = gdk_window_get_height(window);
+}
+
 void wxGTKCairoDCImpl::DoDrawBitmap(const wxBitmap& bitmap, int x, int y, bool useMask)
 {
     wxCHECK_RET(IsOk(), "invalid DC");
@@ -343,9 +349,7 @@ wxPaintDCImpl::wxPaintDCImpl(wxPaintDC* owner, wxWindow* window)
 {
     cairo_t* cr = window->GTKPaintContext();
     wxCHECK_RET(cr, "using wxPaintDC without being in a native paint event");
-    GdkWindow* gdkWindow = gtk_widget_get_window(window->m_wxwindow);
-    m_width = gdk_window_get_width(gdkWindow);
-    m_height = gdk_window_get_height(gdkWindow);
+    InitSize(gtk_widget_get_window(window->m_wxwindow));
     wxGraphicsContext* gc = wxGraphicsContext::CreateFromNative(cr);
     gc->EnableOffset(m_contentScaleFactor <= 1);
     SetGraphicsContext(gc);
@@ -356,8 +360,8 @@ wxScreenDCImpl::wxScreenDCImpl(wxScreenDC* owner)
     : wxGTKCairoDCImpl(owner, 0)
 {
     GdkWindow* window = gdk_get_default_root_window();
-    m_width = gdk_window_get_width(window);
-    m_height = gdk_window_get_height(window);
+    InitSize(window);
+
     cairo_t* cr = gdk_cairo_create(window);
     wxGraphicsContext* gc = wxGraphicsContext::CreateFromNative(cr);
     cairo_destroy(cr);