diff --git a/src/emu/machine/rtc4543.c b/src/emu/machine/rtc4543.c
index 878e6e3cc63..7bd9ad32fd4 100644
--- a/src/emu/machine/rtc4543.c
+++ b/src/emu/machine/rtc4543.c
@@ -96,7 +96,7 @@ void rtc4543_device::rtc_clock_updated(int year, int month, int day, int day_of_
     m_regs[0] = make_bcd(second);               // seconds (BCD, 0-59) in bits 0-6, bit 7 = battery low
     m_regs[1] = make_bcd(minute);               // minutes (BCD, 0-59)
     m_regs[2] = make_bcd(hour);                 // hour (BCD, 0-23)
-    m_regs[3] = make_bcd(weekday[day_of_week]);	// low nibble = day of the week
+    m_regs[3] = make_bcd(weekday[day_of_week-1]);	// low nibble = day of the week
     m_regs[3] |= (make_bcd(day) & 0x0f)<<4;	    // high nibble = low digit of day
     m_regs[4] = (make_bcd(day) >> 4);			// low nibble = high digit of day
     m_regs[4] |= (make_bcd(month & 0x0f)<<4);	// high nibble = low digit of month