diff --git a/setup/extensions.json b/setup/extensions.json
index f5e9067989..8140463c55 100644
--- a/setup/extensions.json
+++ b/setup/extensions.json
@@ -139,6 +139,7 @@
     {
         "name": "winutil",
         "only": "windows",
+        "headers": "calibre/utils/windows/common.h",
         "sources": "calibre/utils/windows/winutil.cpp",
         "libraries": "shell32 wininet advapi32",
         "cflags": "/X"
diff --git a/src/calibre/utils/windows/common.h b/src/calibre/utils/windows/common.h
new file mode 100644
index 0000000000..6cb498b9f1
--- /dev/null
+++ b/src/calibre/utils/windows/common.h
@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2020 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#pragma once
+#define PY_SSIZE_T_CLEAN
+#define UNICODE
+#include <Windows.h>
+#include <Python.h>
+
+class wchar_raii {
+	private:
+		wchar_t *handle;
+		wchar_raii( const wchar_raii & ) ;
+		wchar_raii & operator=( const wchar_raii & ) ;
+
+	public:
+		wchar_raii() : handle(NULL) {}
+
+		~wchar_raii() {
+			if (handle) {
+				PyMem_Free(handle);
+				handle = NULL;
+			}
+		}
+
+		wchar_t *ptr() { return handle; }
+		void set_ptr(wchar_t *val) { handle = val; }
+};
+
+class handle_raii {
+	private:
+		HANDLE handle;
+		handle_raii( const handle_raii & ) ;
+		handle_raii & operator=( const handle_raii & ) ;
+
+	public:
+		handle_raii() : handle(INVALID_HANDLE_VALUE) {}
+		handle_raii(HANDLE h) : handle(h) {}
+
+		~handle_raii() {
+			if (handle != INVALID_HANDLE_VALUE) {
+				CloseHandle(handle);
+				handle = INVALID_HANDLE_VALUE;
+			}
+		}
+
+		HANDLE ptr() const { return handle; }
+		void set_ptr(HANDLE val) { handle = val; }
+		explicit operator bool() const { return handle != INVALID_HANDLE_VALUE; }
+
+};
+
+
+static int
+py_to_wchar(PyObject *obj, wchar_raii *output) {
+	if (!PyUnicode_Check(obj)) {
+		if (obj == Py_None) { return 1; }
+		PyErr_SetString(PyExc_TypeError, "unicode object expected");
+		return 0;
+	}
+    wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
+    if (!buf) { PyErr_NoMemory(); return 0; }
+	output->set_ptr(buf);
+	return 1;
+}
+
+static int
+py_to_wchar_no_none(PyObject *obj, wchar_raii *output) {
+	if (!PyUnicode_Check(obj)) {
+		PyErr_SetString(PyExc_TypeError, "unicode object expected");
+		return 0;
+	}
+    wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
+    if (!buf) { PyErr_NoMemory(); return 0; }
+	output->set_ptr(buf);
+	return 1;
+}
diff --git a/src/calibre/utils/windows/winutil.cpp b/src/calibre/utils/windows/winutil.cpp
index 5472bee295..125cdd5e85 100644
--- a/src/calibre/utils/windows/winutil.cpp
+++ b/src/calibre/utils/windows/winutil.cpp
@@ -5,9 +5,7 @@
  * Distributed under terms of the GPL3 license.
  */
 
-#define PY_SSIZE_T_CLEAN
-#define UNICODE
-#include <Windows.h>
+#include "common.h"
 #include <processthreadsapi.h>
 #include <wininet.h>
 #include <Lmcons.h>
@@ -21,7 +19,6 @@
 #include <comip.h>
 #include <comdef.h>
 #include <atlbase.h>  // for CComPtr
-#include <Python.h>
 #include <versionhelpers.h>
 
 // Handle {{{
@@ -218,49 +215,6 @@ class DeleteFileProgressSink : public IFileOperationProgressSink {  // {{{
   ULONG m_cRef;
 }; // }}}
 
-class wchar_raii {  // {{{
-	private:
-		wchar_t *handle;
-		wchar_raii( const wchar_raii & ) ;
-		wchar_raii & operator=( const wchar_raii & ) ;
-
-	public:
-		wchar_raii() : handle(NULL) {}
-
-		~wchar_raii() {
-			if (handle) {
-				PyMem_Free(handle);
-				handle = NULL;
-			}
-		}
-
-		wchar_t *ptr() { return handle; }
-		void set_ptr(wchar_t *val) { handle = val; }
-}; // }}}
-
-class handle_raii {  // {{{
-	private:
-		HANDLE handle;
-		handle_raii( const handle_raii & ) ;
-		handle_raii & operator=( const handle_raii & ) ;
-
-	public:
-		handle_raii() : handle(INVALID_HANDLE_VALUE) {}
-		handle_raii(HANDLE h) : handle(h) {}
-
-		~handle_raii() {
-			if (handle != INVALID_HANDLE_VALUE) {
-				CloseHandle(handle);
-				handle = INVALID_HANDLE_VALUE;
-			}
-		}
-
-		HANDLE ptr() const { return handle; }
-		void set_ptr(HANDLE val) { handle = val; }
-		explicit operator bool() const { return handle != INVALID_HANDLE_VALUE; }
-
-}; // }}}
-
 class scoped_com_initializer {  // {{{
 	public:
 		scoped_com_initializer() : m_succeded(false) { if (SUCCEEDED(CoInitialize(NULL))) m_succeded = true; }
@@ -272,31 +226,6 @@ class scoped_com_initializer {  // {{{
 		scoped_com_initializer & operator=( const scoped_com_initializer & ) ;
 }; // }}}
 
-// py_to_wchar {{{
-static int
-py_to_wchar(PyObject *obj, wchar_raii *output) {
-	if (!PyUnicode_Check(obj)) {
-		if (obj == Py_None) { return 1; }
-		PyErr_SetString(PyExc_TypeError, "unicode object expected");
-		return 0;
-	}
-    wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
-    if (!buf) { PyErr_NoMemory(); return 0; }
-	output->set_ptr(buf);
-	return 1;
-}
-
-static int
-py_to_wchar_no_none(PyObject *obj, wchar_raii *output) {
-	if (!PyUnicode_Check(obj)) {
-		PyErr_SetString(PyExc_TypeError, "unicode object expected");
-		return 0;
-	}
-    wchar_t *buf = PyUnicode_AsWideCharString(obj, NULL);
-    if (!buf) { PyErr_NoMemory(); return 0; }
-	output->set_ptr(buf);
-	return 1;
-} // }}}
 
 static PyObject *
 winutil_folder_path(PyObject *self, PyObject *args) {