diff --git a/src/mouse_msystems.c b/src/mouse_msystems.c
index baa0aea..9424191 100644
--- a/src/mouse_msystems.c
+++ b/src/mouse_msystems.c
@@ -16,7 +16,7 @@ static void mouse_msystems_poll(int x, int y, int z, int b, void *p)
 {
         mouse_msystems_t *mouse = (mouse_msystems_t *)p;
         SERIAL *serial = mouse->serial;        
-        uint8_t mousedat[4];
+        uint8_t mousedat[5];
 
         if (!x && !y && b == mouse->oldb)
                 return;