diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index 6d57aea..b0eb332 100644
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -512,7 +512,7 @@
 	if (!PyArg_ParseTuple(args, "|l", &bytesrequested))
 		return NULL;
 	if (bytesrequested < 0)
-		buffersize = new_buffersize(f, 0);
+		buffersize = new_buffersize(f, (size_t)0);
 	else
 		buffersize = bytesrequested;
 	v = PyString_FromStringAndSize((char *)NULL, buffersize);