diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -85,6 +85,8 @@
 	.sv_thread_detach = NULL,
 	.sv_trap	= NULL,
 	.sv_stackgap	= elf64_stackgap,
+	.sv_onexec_old = exec_onexec_old,
+	.sv_onexit =	exit_onexit,
 };
 
 struct sysentvec elf64_freebsd_sysvec_la57 = {
@@ -123,6 +125,8 @@
 	.sv_thread_detach = NULL,
 	.sv_trap	= NULL,
 	.sv_stackgap	= elf64_stackgap,
+	.sv_onexec_old = exec_onexec_old,
+	.sv_onexit =	exit_onexit,
 };
 
 static void
diff --git a/sys/compat/ia32/ia32_sysvec.c b/sys/compat/ia32/ia32_sysvec.c
--- a/sys/compat/ia32/ia32_sysvec.c
+++ b/sys/compat/ia32/ia32_sysvec.c
@@ -131,6 +131,8 @@
 	.sv_thread_detach = NULL,
 	.sv_trap	= NULL,
 	.sv_stackgap	= elf32_stackgap,
+	.sv_onexec_old = exec_onexec_old,
+	.sv_onexit =	exit_onexit,
 };
 INIT_SYSENTVEC(elf_ia32_sysvec, &ia32_freebsd_sysvec);
 
diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1040,6 +1040,13 @@
 	}
 }
 
+void
+exec_onexec_old(struct thread *td)
+{
+	sigfastblock_clear(td);
+	umtx_exec(td->td_proc);
+}
+
 /*
  * Destroy old address space, and allocate a new stack.
  *	The new stack is only sgrowsiz large because it is grown
@@ -1062,8 +1069,8 @@
 	imgp->vmspace_destroyed = 1;
 	imgp->sysent = sv;
 
-	sigfastblock_clear(td);
-	umtx_exec(p);
+	if (p->p_sysent->sv_onexec_old != NULL)
+		p->p_sysent->sv_onexec_old(td);
 	itimers_exec(p);
 	if (sv->sv_onexec != NULL)
 		sv->sv_onexec(p, imgp);
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -195,6 +195,13 @@
 	p->p_treeflag &= ~P_TREE_ORPHANED;
 }
 
+void
+exit_onexit(struct proc *p)
+{
+	MPASS(p->p_numthreads == 1);
+	umtx_thread_exit(FIRST_THREAD_IN_PROC(p));
+}
+
 /*
  * exit -- death of process.
  */
@@ -340,9 +347,6 @@
 
 	itimers_exit(p);
 
-	if (p->p_sysent->sv_onexit != NULL)
-		p->p_sysent->sv_onexit(p);
-
 	/*
 	 * Check if any loadable modules need anything done at process exit.
 	 * E.g. SYSV IPC stuff.
@@ -373,7 +377,8 @@
 
 	PROC_UNLOCK(p);
 
-	umtx_thread_exit(td);
+	if (p->p_sysent->sv_onexit != NULL)
+		p->p_sysent->sv_onexit(p);
 	seltdfini(td);
 
 	/*
diff --git a/sys/sys/sysent.h b/sys/sys/sysent.h
--- a/sys/sys/sysent.h
+++ b/sys/sys/sysent.h
@@ -150,6 +150,7 @@
 	u_long		*sv_hwcap2;	/* Value passed in AT_HWCAP2. */
 	const char	*(*sv_machine_arch)(struct proc *);
 	vm_offset_t	sv_fxrng_gen_base;
+	void		(*sv_onexec_old)(struct thread *td);
 	void		(*sv_onexec)(struct proc *, struct image_params *);
 	void		(*sv_onexit)(struct proc *);
 	void		(*sv_ontdexit)(struct thread *td);
@@ -321,6 +322,9 @@
 void exec_sysvec_init_secondary(struct sysentvec *sv, struct sysentvec *sv2);
 void exec_inittk(void);
 
+void exit_onexit(struct proc *p);
+void exec_onexec_old(struct thread *td);
+
 #define INIT_SYSENTVEC(name, sv)					\
     SYSINIT(name, SI_SUB_EXEC, SI_ORDER_ANY,				\
 	(sysinit_cfunc_t)exec_sysvec_init, sv);