diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index 259a4234239..b34dd525926 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -136,7 +136,7 @@ fill_file_fields(PyFileObject *f, FILE *fp, PyObject *name, char *mode,
 static int
 check_the_mode(char *mode)
 {
-	unsigned int len = strlen(mode);
+	size_t len = strlen(mode);
 
 	switch (len) {
 	case 0: