diff --git a/include/wx/private/spinctrl.h b/include/wx/private/spinctrl.h
new file mode 100644
index 0000000000..685e8faf69
--- /dev/null
+++ b/include/wx/private/spinctrl.h
@@ -0,0 +1,27 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/private/spinctrl.h
+// Purpose:     Private functions used in wxSpinCtrl implementation.
+// Author:      Vadim Zeitlin
+// Created:     2019-11-13
+// Copyright:   (c) 2019 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PRIVATE_SPINCTRL_H_
+#define _WX_PRIVATE_SPINCTRL_H_
+
+namespace wxPrivate
+{
+
+// This is an internal helper function currently used by all ports: return the
+// string containing hexadecimal representation of the given number.
+extern wxString wxSpinCtrlFormatAsHex(long val, long maxVal);
+
+// The helper function to determine the best size for the given control.
+// We can't implement this function in the wxSpinCtrlBase because MSW implementation
+// of wxSpinCtrl is derived from wxSpinButton but uses the same algorithm.
+extern wxSize wxSpinCtrlGetBestSize(const wxControl* spin, int minVal, int maxVal, int base);
+
+} // namespace wxPrivate
+
+#endif // _WX_PRIVATE_SPINCTRL_H_
diff --git a/include/wx/spinctrl.h b/include/wx/spinctrl.h
index 0051737fbc..775672f97b 100644
--- a/include/wx/spinctrl.h
+++ b/include/wx/spinctrl.h
@@ -136,19 +136,6 @@ typedef void (wxEvtHandler::*wxSpinDoubleEventFunction)(wxSpinDoubleEvent&);
 #if !defined(wxHAS_NATIVE_SPINCTRL) || !defined(wxHAS_NATIVE_SPINCTRLDOUBLE)
     #include "wx/generic/spinctlg.h"
 #endif
-namespace wxPrivate
-{
-
-// This is an internal helper function currently used by all ports: return the
-// string containing hexadecimal representation of the given number.
-extern wxString wxSpinCtrlFormatAsHex(long val, long maxVal);
-
-// The helper function to determine the best size for the given control.
-// We can't implement this function in the wxSpinCtrlBase because MSW implementation
-// of wxSpinCtrl is derived from wxSpinButton but uses the same algorithm.
-extern wxSize wxSpinCtrlGetBestSize(const wxControl* spin, int minVal, int maxVal, int base);
-
-} // namespace wxPrivate
 
 // old wxEVT_COMMAND_* constants
 #define wxEVT_COMMAND_SPINCTRL_UPDATED         wxEVT_SPINCTRL
diff --git a/src/common/spinctrlcmn.cpp b/src/common/spinctrlcmn.cpp
index 9598ef829d..076e68d15d 100644
--- a/src/common/spinctrlcmn.cpp
+++ b/src/common/spinctrlcmn.cpp
@@ -25,6 +25,8 @@
 #include "wx/spinbutt.h"
 #include "wx/spinctrl.h"
 
+#include "wx/private/spinctrl.h"
+
 #if wxUSE_SPINCTRL
 
 wxDEFINE_EVENT(wxEVT_SPINCTRL, wxSpinEvent);
diff --git a/src/generic/spinctlg.cpp b/src/generic/spinctlg.cpp
index b49c5db77b..3a53802889 100644
--- a/src/generic/spinctlg.cpp
+++ b/src/generic/spinctlg.cpp
@@ -32,6 +32,8 @@
 
 #if wxUSE_SPINCTRL
 
+#include "wx/private/spinctrl.h"
+
 wxIMPLEMENT_DYNAMIC_CLASS(wxSpinDoubleEvent, wxNotifyEvent);
 
 // There are port-specific versions for the wxSpinCtrl, so exclude the
diff --git a/src/gtk/spinctrl.cpp b/src/gtk/spinctrl.cpp
index eaeeea8b3c..ec65588bf5 100644
--- a/src/gtk/spinctrl.cpp
+++ b/src/gtk/spinctrl.cpp
@@ -20,6 +20,8 @@
     #include "wx/wxcrtvararg.h"
 #endif
 
+#include "wx/private/spinctrl.h"
+
 #include "wx/gtk/private.h"
 
 //-----------------------------------------------------------------------------
diff --git a/src/gtk1/spinctrl.cpp b/src/gtk1/spinctrl.cpp
index d462dbe0ca..6c416de7b4 100644
--- a/src/gtk1/spinctrl.cpp
+++ b/src/gtk1/spinctrl.cpp
@@ -21,6 +21,8 @@
     #include "wx/crt.h"
 #endif
 
+#include "wx/private/spinctrl.h"
+
 #include "wx/gtk1/private.h"
 
 //-----------------------------------------------------------------------------
diff --git a/src/msw/spinctrl.cpp b/src/msw/spinctrl.cpp
index 321f6b11c5..72c8cfbb30 100644
--- a/src/msw/spinctrl.cpp
+++ b/src/msw/spinctrl.cpp
@@ -35,6 +35,8 @@
     #include "wx/wxcrtvararg.h"
 #endif
 
+#include "wx/private/spinctrl.h"
+
 #include "wx/msw/private.h"
 #include "wx/msw/private/winstyle.h"