diff --git a/src/mesa/drivers/dri/sis/sis_screen.c b/src/mesa/drivers/dri/sis/sis_screen.c
index ccfa959c9af..e6c398f4e28 100644
--- a/src/mesa/drivers/dri/sis/sis_screen.c
+++ b/src/mesa/drivers/dri/sis/sis_screen.c
@@ -316,6 +316,8 @@ static void sisCopyBuffer( __DRIdrawablePrivate *dPriv )
    int i;
    ENGPACKET stEngPacket;
   
+   memset(&stEngPacket, 0, sizeof(ENGPACKET));
+
    while ((*smesa->FrameCountPtr) - MMIO_READ(0x8a2c) > SIS_MAX_FRAME_LENGTH)
       ;