diff --git a/Include/fileutils.h b/Include/fileutils.h
index 1d8df15..a232460 100644
--- a/Include/fileutils.h
+++ b/Include/fileutils.h
@@ -41,7 +41,8 @@
 #ifdef HAVE_REALPATH
 PyAPI_FUNC(wchar_t*) _Py_wrealpath(
     const wchar_t *path,
-    wchar_t *resolved_path);
+    wchar_t *resolved_path,
+    size_t resolved_path_size);
 #endif
 
 PyAPI_FUNC(wchar_t*) _Py_wgetcwd(
diff --git a/Python/fileutils.c b/Python/fileutils.c
index bd6ab5d..502868f 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -321,7 +321,8 @@
 
 #ifdef HAVE_REALPATH
 wchar_t*
-_Py_wrealpath(const wchar_t *path, wchar_t *resolved_path)
+_Py_wrealpath(const wchar_t *path,
+              wchar_t *resolved_path, size_t resolved_path_size)
 {
     char *cpath;
     char cresolved_path[PATH_MAX];
@@ -336,7 +337,7 @@
     PyMem_Free(cpath);
     if (res == NULL)
         return NULL;
-    r = mbstowcs(resolved_path, cresolved_path, PATH_MAX);
+    r = mbstowcs(resolved_path, cresolved_path, resolved_path_size);
     if (r == (size_t)-1 || r >= PATH_MAX) {
         errno = EINVAL;
         return NULL;
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 1eba28e..d02ee5b 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1742,7 +1742,7 @@
 #else /* All other filename syntaxes */
     if (_HAVE_SCRIPT_ARGUMENT(argc, argv)) {
 #if defined(HAVE_REALPATH)
-        if (_Py_wrealpath(argv0, fullpath)) {
+        if (_Py_wrealpath(argv0, fullpath, PATH_MAX)) {
             argv0 = fullpath;
         }
 #endif