Index: sys/dev/pci/pci_pci.c
===================================================================
--- sys/dev/pci/pci_pci.c
+++ sys/dev/pci/pci_pci.c
@@ -2545,6 +2545,20 @@
 int
 pcib_maxslots(device_t dev)
 {
+	uint32_t pcie_pos;
+	uint16_t val;
+
+	/*
+	 * If this is a PCIe rootport or downstream switch port, there's only
+	 * one slot permitted.
+	 */
+	if (pci_find_cap(dev, PCIY_EXPRESS, &pcie_pos) == 0) {
+		val = pci_read_config(dev, pcie_pos + PCIER_FLAGS, 2);
+		val &= PCIEM_FLAGS_TYPE;
+		if (val == PCIEM_TYPE_ROOT_PORT ||
+		    val == PCIEM_TYPE_DOWNSTREAM_PORT)
+			return (0);
+	}
 	return (PCI_SLOTMAX);
 }
 
@@ -2558,7 +2572,7 @@
 	if (sc->flags & PCIB_ENABLE_ARI)
 		return (PCIE_ARI_SLOTMAX);
 	else
-		return (PCI_SLOTMAX);
+		return (pcib_maxslots(dev));
 }
 
 static int