diff --git a/interface/wx/renderer.h b/interface/wx/renderer.h
index 2a3772b78a..ddd4d3a1f8 100644
--- a/interface/wx/renderer.h
+++ b/interface/wx/renderer.h
@@ -552,7 +552,9 @@ public:
 
     /**
         Returns the size of a check box.
-        The @a win parameter is not used currently and can be @NULL.
+
+        @param win A valid, i.e. non-null, window pointer which is used to get
+            the theme defining the checkbox size under some platforms.
     */
     virtual wxSize GetCheckBoxSize(wxWindow* win) = 0;
 
diff --git a/src/generic/renderg.cpp b/src/generic/renderg.cpp
index fc2f39645d..eb5e1442c4 100644
--- a/src/generic/renderg.cpp
+++ b/src/generic/renderg.cpp
@@ -714,6 +714,8 @@ wxRendererGeneric::DrawCheckBox(wxWindow *WXUNUSED(win),
 
 wxSize wxRendererGeneric::GetCheckBoxSize(wxWindow *win)
 {
+    wxCHECK_MSG( win, wxSize(0, 0), "Must have a valid window" );
+
     return win->FromDIP(wxSize(16, 16));
 }
 
diff --git a/src/gtk/renderer.cpp b/src/gtk/renderer.cpp
index 1c425261dc..a65d6f27f6 100644
--- a/src/gtk/renderer.cpp
+++ b/src/gtk/renderer.cpp
@@ -551,8 +551,13 @@ wxRendererGTK::DrawComboBoxDropButton(wxWindow *win,
 }
 
 wxSize
-wxRendererGTK::GetCheckBoxSize(wxWindow *WXUNUSED(win))
+wxRendererGTK::GetCheckBoxSize(wxWindow* win)
 {
+    // Even though we don't use the window in this implementation, still check
+    // that it's valid to avoid surprises when running the same code under the
+    // other platforms.
+    wxCHECK_MSG( win, wxSize(0, 0), "Must have a valid window" );
+
 #ifdef __WXGTK3__
     int min_width, min_height;
     wxGtkStyleContext sc;
diff --git a/src/msw/renderer.cpp b/src/msw/renderer.cpp
index d94f0c582f..6d529a1946 100644
--- a/src/msw/renderer.cpp
+++ b/src/msw/renderer.cpp
@@ -521,8 +521,12 @@ wxRendererMSW::DrawTitleBarBitmap(wxWindow *win,
     DoDrawFrameControl(DFC_CAPTION, kind, win, dc, rect, flags);
 }
 
-wxSize wxRendererMSW::GetCheckBoxSize(wxWindow * WXUNUSED(win))
+wxSize wxRendererMSW::GetCheckBoxSize(wxWindow* win)
 {
+    // Even though we don't use the window in this implementation, still check
+    // that it's valid to avoid surprises when using themes.
+    wxCHECK_MSG( win, wxSize(0, 0), "Must have a valid window" );
+
     return wxSize(::GetSystemMetrics(SM_CXMENUCHECK),
                   ::GetSystemMetrics(SM_CYMENUCHECK));
 }
@@ -830,6 +834,8 @@ wxRendererXP::DrawTitleBarBitmap(wxWindow *win,
 
 wxSize wxRendererXP::GetCheckBoxSize(wxWindow* win)
 {
+    wxCHECK_MSG( win, wxSize(0, 0), "Must have a valid window" );
+
     wxUxThemeHandle hTheme(win, L"BUTTON");
     if (hTheme)
     {
diff --git a/src/osx/carbon/renderer.cpp b/src/osx/carbon/renderer.cpp
index 0f777377ac..aa124a816d 100644
--- a/src/osx/carbon/renderer.cpp
+++ b/src/osx/carbon/renderer.cpp
@@ -484,8 +484,13 @@ wxRendererMac::DrawCheckBox(wxWindow *win,
                        kind, kThemeAdornmentNone);
 }
 
-wxSize wxRendererMac::GetCheckBoxSize(wxWindow* WXUNUSED(win))
+wxSize wxRendererMac::GetCheckBoxSize(wxWindow* win)
 {
+    // Even though we don't use the window in this implementation, still check
+    // that it's valid to avoid surprises when running the same code under the
+    // other platforms.
+    wxCHECK_MSG( win, wxSize(0, 0), "Must have a valid window" );
+
     wxSize size;
     SInt32 width, height;
     OSStatus errStatus;