diff --git a/os/io.c b/os/io.c
index 19a449ad8..d04ebd895 100644
--- a/os/io.c
+++ b/os/io.c
@@ -132,8 +132,8 @@ static OsCommPtr AvailableInput = (OsCommPtr) NULL;
 				  ((xBigReq *)(req))->length)
 
 #define MAX_TIMES_PER         10
-#define BUFSIZE 4096
-#define BUFWATERMARK 8192
+#define BUFSIZE 16384
+#define BUFWATERMARK 32768
 
 /*
  *   A lot of the code in this file manipulates a ConnectionInputPtr: