diff --git a/sys/dev/disk/sdhci/sdhci_pci.c b/sys/dev/disk/sdhci/sdhci_pci.c
--- a/sys/dev/disk/sdhci/sdhci_pci.c
+++ b/sys/dev/disk/sdhci/sdhci_pci.c
@@ -428,8 +428,13 @@
 	    rman_get_rid(sc->irq_res), sc->irq_res);
 	pci_release_msi(dev);
 
-	for (i = 0; i < sc->num_slots; i++) {
-		struct sdhci_slot *slot = &sc->slots[i];
+	/* mem_res[] is indexed by BAR slot position which can have gaps
+	 * if a slot failed during attach; iterate by BAR position. */
+	for (i = 0; i < 6; i++) {
+		struct sdhci_slot *slot;
+		if (sc->mem_res[i] == NULL)
+			continue;
+		slot = &sc->slots[i];
 
 		sdhci_cleanup_slot(slot);
 		bus_release_resource(dev, SYS_RES_MEMORY,