diff --git a/drivers/3dfx.h b/drivers/3dfx.h
index f784f7d34c..1eb54f6d82 100644
--- a/drivers/3dfx.h
+++ b/drivers/3dfx.h
@@ -316,7 +316,7 @@ typedef struct voodoo_yuv_fb_t voodoo_yuv_fb;
 #define TDFXF_HSYNC_MASK		0x03
 #define TDFXF_VSYNC_MASK		0x0c
 
-#define XYREG(x,y)		(((((unsigned long)y) & 0xFFFF) << 16) | (((unsigned long)x) & 0xFFFF))
+#define XYREG(x,y)		(((((unsigned long)y) & 0x1FFF) << 16) | (((unsigned long)x) & 0x1FFF))
 
 //#define TDFXFB_DEBUG 
 #ifdef TDFXFB_DEBUG