diff --git a/kernel/fork.c b/kernel/fork.c
index 0166697..de5c16c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1696,7 +1696,12 @@
 				CLONE_NEWNET))
 		goto bad_unshare_out;
 
-	if (unshare_flags & CLONE_SYSVSEM)
+	/*
+	 * CLONE_NEWIPC must also detach from the undolist: after switching
+	 * to a new ipc namespace, the semaphore arrays from the old
+	 * namespace are unreachable.
+	 */
+	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))
 		do_sysvsem = 1;
 	if ((err = unshare_thread(unshare_flags)))
 		goto bad_unshare_out;