diff --git a/sys/amd64/acpica/madt.c b/sys/amd64/acpica/madt.c
index 34ee38720000..a88d183d9746 100644
--- a/sys/amd64/acpica/madt.c
+++ b/sys/amd64/acpica/madt.c
@@ -367,7 +367,7 @@ madt_setup_io(void)
 	}
 		    
 	/* First, we run through adding I/O APIC's. */
-	if (madt->PCATCompat)
+	if (madt->PCATCompat && !(acpi_quirks & ACPI_Q_MADT_IRQ0))
 		ioapic_enable_mixed_mode();
 	madt_walk_table(madt_parse_apics, NULL);
 
@@ -596,8 +596,14 @@ madt_parse_interrupt_override(MADT_INTERRUPT_OVERRIDE *intr)
 	enum intr_polarity pol;
 	char buf[64];
 
+	if (acpi_quirks & ACPI_Q_MADT_IRQ0 && intr->Source == 0 &&
+	    intr->Interrupt == 2) {
+		if (bootverbose)
+			printf("MADT: Skipping timer override\n");
+		return;
+	}
 	if (bootverbose)
-		printf("MADT: intr override: source %u, irq %u\n",
+		printf("MADT: Interrupt override: source %u, irq %u\n",
 		    intr->Source, intr->Interrupt);
 	KASSERT(intr->Bus == 0, ("bus for interrupt overrides must be zero"));
 	if (madt_find_interrupt(intr->Interrupt, &new_ioapic,
diff --git a/sys/dev/acpica/acpivar.h b/sys/dev/acpica/acpivar.h
index 4478252b6fd8..fc800e5cdcee 100644
--- a/sys/dev/acpica/acpivar.h
+++ b/sys/dev/acpica/acpivar.h
@@ -160,11 +160,20 @@ extern struct mtx			acpi_mutex;
 #define	ACPI_INTR_APIC		1
 #define	ACPI_INTR_SAPIC		2
 
-/* Quirk flags. */
+/*
+ * Quirk flags.
+ *
+ * ACPI_Q_BROKEN: Disables all ACPI support.
+ * ACPI_Q_TIMER: Disables support for the ACPI timer.
+ * ACPI_Q_MADT_IRQ0: Specifies that ISA IRQ 0 is wired up to pin 0 of the
+ *	first APIC and that the MADT should force that by ignoring the PC-AT
+ *	compatible flag and ignoring overrides that redirect IRQ 0 to pin 2.
+ */
 extern int	acpi_quirks;
 #define ACPI_Q_OK		0
-#define ACPI_Q_BROKEN		(1 << 0)	/* Disable ACPI completely. */
-#define ACPI_Q_TIMER		(1 << 1)	/* Disable ACPI timer. */
+#define ACPI_Q_BROKEN		(1 << 0)
+#define ACPI_Q_TIMER		(1 << 1)
+#define ACPI_Q_MADT_IRQ0	(1 << 2)
 
 /*
  * Note that the low ivar values are reserved to provide
diff --git a/sys/i386/acpica/madt.c b/sys/i386/acpica/madt.c
index 43a0a885402a..22598e0f52bd 100644
--- a/sys/i386/acpica/madt.c
+++ b/sys/i386/acpica/madt.c
@@ -367,7 +367,7 @@ madt_setup_io(void)
 	}
 		    
 	/* First, we run through adding I/O APIC's. */
-	if (madt->PCATCompat)
+	if (madt->PCATCompat && !(acpi_quirks & ACPI_Q_MADT_IRQ0))
 		ioapic_enable_mixed_mode();
 	madt_walk_table(madt_parse_apics, NULL);
 
@@ -595,8 +595,14 @@ madt_parse_interrupt_override(MADT_INTERRUPT_OVERRIDE *intr)
 	enum intr_polarity pol;
 	char buf[64];
 
+	if (acpi_quirks & ACPI_Q_MADT_IRQ0 && intr->Source == 0 &&
+	    intr->Interrupt == 2) {
+		if (bootverbose)
+			printf("MADT: Skipping timer override\n");
+		return;
+	}
 	if (bootverbose)
-		printf("MADT: intr override: source %u, irq %u\n",
+		printf("MADT: Interrupt override: source %u, irq %u\n",
 		    intr->Source, intr->Interrupt);
 	KASSERT(intr->Bus == 0, ("bus for interrupt overrides must be zero"));
 	if (madt_find_interrupt(intr->Interrupt, &new_ioapic,