diff --git a/sys/dev/pci/pci.c b/sys/dev/pci/pci.c
--- a/sys/dev/pci/pci.c
+++ b/sys/dev/pci/pci.c
@@ -1927,7 +1927,11 @@
 		}
 	}
 
-	/* Mask all vectors. */
+	/*
+	 * Mask all vectors. Note that the message index assertion in
+	 * pci_mask_msix requires msix_ctrl to be set.
+	 */
+	cfg->msix.msix_ctrl = ctrl;
 	for (i = 0; i < msgnum; i++)
 		pci_mask_msix(child, i);