-#define RXFSIDH(n) ((n) * 4)
-#define RXFSIDL(n) ((n) * 4 + 1)
-#define RXFEID8(n) ((n) * 4 + 2)
-#define RXFEID0(n) ((n) * 4 + 3)
+#define RXFSID(n) ((n < 3) ? 0 : 4)
+#define RXFSIDH(n) ((n) * 4 + RXFSID(n))
+#define RXFSIDL(n) ((n) * 4 + 1 + RXFSID(n))
+#define RXFEID8(n) ((n) * 4 + 2 + RXFSID(n))
+#define RXFEID0(n) ((n) * 4 + 3 + RXFSID(n))