Index: head/sys/kern/kern_sig.c
===================================================================
--- head/sys/kern/kern_sig.c
+++ head/sys/kern/kern_sig.c
@@ -2847,6 +2847,8 @@
 			sig = ptracestop(td, sig, &ksi);
 			mtx_lock(&ps->ps_mtx);
 
+			td->td_si.si_signo = 0;
+
 			/* 
 			 * Keep looking if the debugger discarded or
 			 * replaced the signal.
Index: head/tests/sys/kern/ptrace_test.c
===================================================================
--- head/tests/sys/kern/ptrace_test.c
+++ head/tests/sys/kern/ptrace_test.c
@@ -3772,6 +3772,78 @@
 }
 #endif
 
+/*
+ * Verify that PT_LWPINFO doesn't return stale siginfo.
+ */
+ATF_TC_WITHOUT_HEAD(ptrace__PT_LWPINFO_stale_siginfo);
+ATF_TC_BODY(ptrace__PT_LWPINFO_stale_siginfo, tc)
+{
+	struct ptrace_lwpinfo pl;
+	pid_t fpid, wpid;
+	int events, status;
+
+	ATF_REQUIRE((fpid = fork()) != -1);
+	if (fpid == 0) {
+		trace_me();
+		raise(SIGABRT);
+		exit(1);
+	}
+
+	/* The first wait() should report the stop from SIGSTOP. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGSTOP);
+
+	ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+	/* The next stop should report the SIGABRT in the child body. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGABRT);
+
+	ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+	ATF_REQUIRE(pl.pl_flags & PL_FLAG_SI);
+	ATF_REQUIRE(pl.pl_siginfo.si_signo == SIGABRT);
+
+	/*
+	 * Continue the process ignoring the signal, but enabling
+	 * syscall traps.
+	 */
+	ATF_REQUIRE(ptrace(PT_SYSCALL, fpid, (caddr_t)1, 0) == 0);
+
+	/*
+	 * The next stop should report a system call entry from
+	 * exit().  PL_FLAGS_SI should not be set.
+	 */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(wpid == fpid);
+	ATF_REQUIRE(WIFSTOPPED(status));
+	ATF_REQUIRE(WSTOPSIG(status) == SIGTRAP);
+
+	ATF_REQUIRE(ptrace(PT_LWPINFO, wpid, (caddr_t)&pl, sizeof(pl)) != -1);
+	ATF_REQUIRE(pl.pl_flags & PL_FLAG_SCE);
+	ATF_REQUIRE((pl.pl_flags & PL_FLAG_SI) == 0);
+
+	/* Disable syscall tracing and continue the child to let it exit. */
+	ATF_REQUIRE(ptrace(PT_GET_EVENT_MASK, fpid, (caddr_t)&events,
+	    sizeof(events)) == 0);
+	events &= ~PTRACE_SYSCALL;
+	ATF_REQUIRE(ptrace(PT_SET_EVENT_MASK, fpid, (caddr_t)&events,
+	    sizeof(events)) == 0);
+	ATF_REQUIRE(ptrace(PT_CONTINUE, fpid, (caddr_t)1, 0) == 0);
+
+	/* The last event should be for the child process's exit. */
+	wpid = waitpid(fpid, &status, 0);
+	ATF_REQUIRE(WIFEXITED(status));
+	ATF_REQUIRE(WEXITSTATUS(status) == 1);
+
+	wpid = wait(&status);
+	ATF_REQUIRE(wpid == -1);
+	ATF_REQUIRE(errno == ECHILD);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 
@@ -3831,6 +3903,7 @@
 #if defined(HAVE_BREAKPOINT) && defined(SKIP_BREAK)
 	ATF_TP_ADD_TC(tp, ptrace__PT_CONTINUE_different_thread);
 #endif
+	ATF_TP_ADD_TC(tp, ptrace__PT_LWPINFO_stale_siginfo);
 
 	return (atf_no_error());
 }