diff --git a/sys/dev/acpica/acpi.c b/sys/dev/acpica/acpi.c
index 7d1fc10afb9..61df797c739 100644
--- a/sys/dev/acpica/acpi.c
+++ b/sys/dev/acpica/acpi.c
@@ -1367,8 +1367,17 @@ acpi_sysres_alloc(device_t dev)
 }
 
 /*
- * Reserve declared resources for devices found during attach once system
- * resources have been allocated.
+ * Reserve declared resources for active devices found during the
+ * namespace scan once the boot-time attach of devices has completed.
+ *
+ * Ideally reserving firmware-assigned resources would work in a
+ * depth-first traversal of the device namespace, but this is
+ * complicated.  In particular, not all resources are enumerated by
+ * ACPI (e.g. PCI bridges and devices enumerate their resources via
+ * other means).  Some systems also enumerate devices via ACPI behind
+ * PCI bridges but without a matching a PCI device_t enumerated via
+ * PCI bus scanning, the device_t's end up as direct children of
+ * acpi0.  Doing this scan late is not ideal, but works for now.
  */
 static void
 acpi_reserve_resources(device_t dev)
@@ -2256,9 +2265,6 @@ acpi_probe_children(device_t bus)
     /* Pre-allocate resources for our rman from any sysresource devices. */
     acpi_sysres_alloc(bus);
 
-    /* Reserve resources already allocated to children. */
-    acpi_reserve_resources(bus);
-
     /* Create any static children by calling device identify methods. */
     ACPI_DEBUG_PRINT((ACPI_DB_OBJECTS, "device identify routines\n"));
     bus_generic_probe(bus);
@@ -2267,6 +2273,12 @@ acpi_probe_children(device_t bus)
     ACPI_DEBUG_PRINT((ACPI_DB_OBJECTS, "acpi bus_generic_attach\n"));
     bus_generic_attach(bus);
 
+    /*
+     * Reserve resources allocated to children but not yet allocated
+     * by a driver.
+     */
+    acpi_reserve_resources(bus);
+
     /* Attach wake sysctls. */
     acpi_wake_sysctl_walk(bus);