diff --git a/hw/isa/piix4.c b/hw/isa/piix4.c
index f876c71750..fc3c8b3fd1 100644
--- a/hw/isa/piix4.c
+++ b/hw/isa/piix4.c
@@ -216,7 +216,7 @@ static void piix4_realize(PCIDevice *dev, Error **errp)
     if (!qdev_realize(DEVICE(&s->rtc), BUS(isa_bus), errp)) {
         return;
     }
-    isa_init_irq(ISA_DEVICE(&s->rtc), &s->rtc.irq, RTC_ISA_IRQ);
+    isa_init_irq(ISA_DEVICE(&s->rtc), &s->rtc.irq, s->rtc.isairq);
 }
 
 static void piix4_init(Object *obj)
diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
index ac9a60c90e..f235c2ddbe 100644
--- a/hw/rtc/mc146818rtc.c
+++ b/hw/rtc/mc146818rtc.c
@@ -912,6 +912,11 @@ static void rtc_realizefn(DeviceState *dev, Error **errp)
         s->base_year = 0;
     }
 
+    if (s->isairq >= ISA_NUM_IRQS) {
+        error_setg(errp, "Maximum value for \"irq\" is: %u", ISA_NUM_IRQS - 1);
+        return;
+    }
+
     rtc_set_date_from_host(isadev);
 
     switch (s->lost_tick_policy) {
@@ -957,15 +962,17 @@ ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, qemu_irq intercept_irq)
 {
     DeviceState *dev;
     ISADevice *isadev;
+    RTCState *s;
 
     isadev = isa_new(TYPE_MC146818_RTC);
     dev = DEVICE(isadev);
+    s = MC146818_RTC(isadev);
     qdev_prop_set_int32(dev, "base_year", base_year);
     isa_realize_and_unref(isadev, bus, &error_fatal);
     if (intercept_irq) {
         qdev_connect_gpio_out(dev, 0, intercept_irq);
     } else {
-        isa_connect_gpio_out(isadev, 0, RTC_ISA_IRQ);
+        isa_connect_gpio_out(isadev, 0, s->isairq);
     }
 
     object_property_add_alias(qdev_get_machine(), "rtc-time", OBJECT(isadev),
@@ -976,6 +983,7 @@ ISADevice *mc146818_rtc_init(ISABus *bus, int base_year, qemu_irq intercept_irq)
 
 static Property mc146818rtc_properties[] = {
     DEFINE_PROP_INT32("base_year", RTCState, base_year, 1980),
+    DEFINE_PROP_UINT8("irq", RTCState, isairq, RTC_ISA_IRQ),
     DEFINE_PROP_LOSTTICKPOLICY("lost_tick_policy", RTCState,
                                lost_tick_policy, LOST_TICK_POLICY_DISCARD),
     DEFINE_PROP_END_OF_LIST(),
@@ -1011,6 +1019,7 @@ static void rtc_reset_hold(Object *obj)
 
 static void rtc_build_aml(ISADevice *isadev, Aml *scope)
 {
+    RTCState *s = MC146818_RTC(isadev);
     Aml *dev;
     Aml *crs;
 
@@ -1021,7 +1030,7 @@ static void rtc_build_aml(ISADevice *isadev, Aml *scope)
     crs = aml_resource_template();
     aml_append(crs, aml_io(AML_DECODE16, RTC_ISA_BASE, RTC_ISA_BASE,
                            0x01, 0x08));
-    aml_append(crs, aml_irq_no_flags(RTC_ISA_IRQ));
+    aml_append(crs, aml_irq_no_flags(s->isairq));
 
     dev = aml_device("RTC");
     aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0B00")));
diff --git a/include/hw/rtc/mc146818rtc.h b/include/hw/rtc/mc146818rtc.h
index 5b45b22924..deef93f89a 100644
--- a/include/hw/rtc/mc146818rtc.h
+++ b/include/hw/rtc/mc146818rtc.h
@@ -25,6 +25,7 @@ struct RTCState {
     MemoryRegion coalesced_io;
     uint8_t cmos_data[128];
     uint8_t cmos_index;
+    uint8_t isairq;
     int32_t base_year;
     uint64_t base_rtc;
     uint64_t last_update;