diff --git a/sys/vfs/hammer/hammer_ioctl.c b/sys/vfs/hammer/hammer_ioctl.c
--- a/sys/vfs/hammer/hammer_ioctl.c
+++ b/sys/vfs/hammer/hammer_ioctl.c
@@ -211,8 +211,10 @@
 		}
 		break;
 	case HAMMERIOC_LIST_VOLUMES:
-		error = hammer_ioc_volume_list(&trans, ip,
-		    (struct hammer_ioc_volume_list *)data);
+		if (error == 0) {
+			error = hammer_ioc_volume_list(&trans, ip,
+			    (struct hammer_ioc_volume_list *)data);
+		}
 		break;
 	case HAMMERIOC_ADD_SNAPSHOT:
 		if (error == 0 && hmp->ronly)