diff --git a/Include/fileutils.h b/Include/fileutils.h
index a232460ef86..cb15936611b 100644
--- a/Include/fileutils.h
+++ b/Include/fileutils.h
@@ -6,7 +6,7 @@ extern "C" {
 #endif
 
 PyAPI_FUNC(wchar_t *) _Py_char2wchar(
-    char *arg);
+    const char *arg);
 
 PyAPI_FUNC(char*) _Py_wchar2char(
     const wchar_t *text);
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 564e2c085be..076f510debd 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -17,7 +17,7 @@
    PyMem_Free() to free the memory), or NULL on error (conversion error or
    memory error). */
 wchar_t*
-_Py_char2wchar(char* arg)
+_Py_char2wchar(const char* arg)
 {
     wchar_t *res;
 #ifdef HAVE_BROKEN_MBSTOWCS