diff --git a/sys/dev/acpica/acpi_hpet.c b/sys/dev/acpica/acpi_hpet.c
index efe57472c404..97fe991f40aa 100644
--- a/sys/dev/acpica/acpi_hpet.c
+++ b/sys/dev/acpica/acpi_hpet.c
@@ -303,6 +303,23 @@ hpet_find(ACPI_HANDLE handle, UINT32 level, void *context,
 	return (AE_OK);
 }
 
+/*
+ * Find an existing IRQ resource that matches the requested IRQ range
+ * and return its RID.  If one is not found, use a new RID.
+ */
+static int
+hpet_find_irq_rid(device_t dev, u_long start, u_long end)
+{
+	u_long irq;
+	int error, rid;
+
+	for (rid = 0;; rid++) {
+		error = bus_get_resource(dev, SYS_RES_IRQ, rid, &irq, NULL);
+		if (error != 0 || (start <= irq && irq <= end))
+			return (rid);
+	}
+}
+
 /* Discover the HPET via the ACPI table of the same name. */
 static void 
 hpet_identify(driver_t *driver, device_t parent)
@@ -540,6 +557,7 @@ hpet_attach(device_t dev)
 			dvectors &= ~(1 << t->irq);
 		}
 		if (t->irq >= 0) {
+			t->intr_rid = hpet_find_irq_rid(dev, t->irq, t->irq);
 			if (!(t->intr_res =
 			    bus_alloc_resource(dev, SYS_RES_IRQ, &t->intr_rid,
 			    t->irq, t->irq, 1, RF_ACTIVE))) {
@@ -590,12 +608,12 @@ hpet_attach(device_t dev)
 	}
 	bus_write_4(sc->mem_res, HPET_ISR, 0xffffffff);
 	sc->irq = -1;
-	sc->intr_rid = -1;
 	/* If at least one timer needs legacy IRQ - set it up. */
 	if (sc->useirq) {
 		j = i = fls(cvectors) - 1;
 		while (j > 0 && (cvectors & (1 << (j - 1))) != 0)
 			j--;
+		sc->intr_rid = hpet_find_irq_rid(dev, j, i);
 		if (!(sc->intr_res = bus_alloc_resource(dev, SYS_RES_IRQ,
 		    &sc->intr_rid, j, i, 1, RF_SHAREABLE | RF_ACTIVE)))
 			device_printf(dev,"Can't map interrupt.\n");