diff --git a/src/device/kbc_at.c b/src/device/kbc_at.c
index dd9ac641c..4c0ea4155 100644
--- a/src/device/kbc_at.c
+++ b/src/device/kbc_at.c
@@ -2269,7 +2269,9 @@ read_p1(atkbc_t *dev)
               Compaq: Reserved;
               NCR: DMA mode.
      */
-    uint8_t ret = machine_get_p1(dev->p1);
+    uint8_t ret = machine_get_p1(dev->p1) | (dev->p1 & 0x03);
+
+    dev->p1 = ((dev->p1 + 1) & 0x03) | (dev->p1 & 0xfc);
 
     return ret;
 }
@@ -2367,14 +2369,7 @@ kbc_at_process_cmd(void *priv)
                 if (machine_has_flags_ex(MACHINE_PS2_KBC)) {
                     if (dev->state != STATE_RESET) {
                         kbc_at_log("ATkbc: self-test reinitialization\n");
-                        /*
-                           Yes, the firmware has an OR, but we need to make sure
-                           to keep any forcibly lowered bytes lowered.
-
-                           TODO: Proper P1 implementation, with OR and AND flags
-                                 in the machine table.
-                         */
-                        dev->p1 = dev->p1 & 0xff;
+                        dev->p1 |= 0xff;
                         write_p2(dev, 0x4b);
                         if (dev->irq[1] != 0xffff)
                             picintc(1 << dev->irq[1]);
@@ -2394,14 +2389,7 @@ kbc_at_process_cmd(void *priv)
                 } else {
                     if (dev->state != STATE_RESET) {
                         kbc_at_log("ATkbc: self-test reinitialization\n");
-                        /*
-                           Yes, the firmware has an OR, but we need to make sure
-                           to keep any forcibly lowered bytes lowered.
-
-                           TODO: Proper P1 implementation, with OR and AND flags
-                                 in the machine table.
-                         */
-                        dev->p1 = dev->p1 & 0xff;
+                        dev->p1 |= 0xff;
                         write_p2(dev, 0xcf);
                         if (dev->irq[0] != 0xffff)
                             picintclevel(1 << dev->irq[0], &dev->irq_state);
diff --git a/src/machine/machine.c b/src/machine/machine.c
index 3e47b1113..50b0bb150 100644
--- a/src/machine/machine.c
+++ b/src/machine/machine.c
@@ -140,6 +140,7 @@ machine_init(void)
 {
     bios_only = 0;
 
+    machine_set_p1_default(machines[machine].kbc_p1);
     machine_set_ps2();
 
     (void) machine_init_ex(machine);
diff --git a/src/machine/machine_table.c b/src/machine/machine_table.c
index 064e60aa8..11a5cbade 100644
--- a/src/machine/machine_table.c
+++ b/src/machine/machine_table.c
@@ -19831,7 +19831,8 @@ machine_generic_p1_handler(void)
 uint8_t
 machine_get_p1(uint8_t kbc_p1)
 {
-    uint8_t ret = 0xff;
+    uint8_t low_bits = ((machine_p1 >> 8) + 1) & 0x03;
+    uint8_t ret      = 0xff;
 
     if (machines[machine].p1_handler)
         ret = machines[machine].p1_handler();
@@ -19844,6 +19845,8 @@ machine_get_p1(uint8_t kbc_p1)
 
     ret &= kbc_p1;
 
+    machine_p1 = (machine_p1 & 0xfffffcff) | (low_bits << 8);
+
     return ret;
 }