diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index 85c2e65856..0787a0268d 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -362,10 +362,10 @@ static void pram_update(MOS6522Q800VIA1State *v1s)
  *
  * Command byte    Register addressed by the command
  *
- * z0000001        Seconds register 0 (lowest-order byte)
- * z0000101        Seconds register 1
- * z0001001        Seconds register 2
- * z0001101        Seconds register 3 (highest-order byte)
+ * z00x0001        Seconds register 0 (lowest-order byte)
+ * z00x0101        Seconds register 1
+ * z00x1001        Seconds register 2
+ * z00x1101        Seconds register 3 (highest-order byte)
  * 00110001        Test register (write-only)
  * 00110101        Write-Protect Register (write-only)
  * z010aa01        RAM address 100aa ($10-$13) (first 20 bytes only)
@@ -373,6 +373,7 @@ static void pram_update(MOS6522Q800VIA1State *v1s)
  * z0111aaa        Extended memory designator and sector number
  *
  * For a read request, z=1, for a write z=0
+ * The letter x indicates don't care
  * The letter a indicates bits whose value depend on what parameter
  * RAM byte you want to address
  */
@@ -389,7 +390,7 @@ static int via1_rtc_compact_cmd(uint8_t value)
     }
     if ((value & 0x03) == 0x01) {
         value >>= 2;
-        if ((value & 0x1c) == 0) {
+        if ((value & 0x18) == 0) {
             /* seconds registers */
             return read | (REG_0 + (value & 0x03));
         } else if ((value == 0x0c) && !read) {