diff --git a/src/libpmemobj/ulog.c b/src/libpmemobj/ulog.c
index 71298f33e9c619976931fc319fc67f0b67df8254..7623129a88cf9281ac0d0f66f724c9653c4b1486 100644
--- a/src/libpmemobj/ulog.c
+++ b/src/libpmemobj/ulog.c
@@ -749,6 +749,10 @@ ulog_clobber_data(struct ulog *ulog_first,
 		 */
 		ulog_inc_gen_num(ulog_second, NULL);
 
+	/* The ULOG_ANY_USER_BUFFER flag indicates more than one ulog exist */
+	if (flags & ULOG_ANY_USER_BUFFER)
+		ASSERTne(ulog_second, NULL);
+
 	struct ulog *u;
 	/*
 	 * only if there was any user buffer it make sense to check