Index: sys/kern/kern_fork.c
===================================================================
--- sys/kern/kern_fork.c	(revision 230617)
+++ sys/kern/kern_fork.c	(working copy)
@@ -797,6 +797,10 @@
 
 	p1 = td->td_proc;
 
+	/* Don't do vfork while being traced. */
+	if (p1->p_flag & P_TRACED)
+		flags &= ~(RFPPWAIT | RFMEM);
+
 	/*
 	 * Here we don't create a new process, but we divorce
 	 * certain parts of a process from itself.