diff --git a/win32/sendmail.c b/win32/sendmail.c
index 025c56a2088..432ebf097d9 100644
--- a/win32/sendmail.c
+++ b/win32/sendmail.c
@@ -868,7 +868,7 @@ static int Post(LPCSTR msg)
 //********************************************************************/
 static int Ack(char **server_response)
 {
-	static char buf[MAIL_BUFFER_SIZE];
+	ZEND_TLS char buf[MAIL_BUFFER_SIZE];
 	int rlen;
 	int Index = 0;
 	int Received = 0;