diff --git a/usr.bin/truss/setup.c b/usr.bin/truss/setup.c
--- a/usr.bin/truss/setup.c
+++ b/usr.bin/truss/setup.c
@@ -205,12 +205,25 @@
 static void
 detach_proc(pid_t pid)
 {
+	int sig, status;
 
-	/* stop the child so that we can detach */
+	/*
+	 * Stop the child so that we can detach.  Filter out possible
+	 * lingering SIGTRAP events buffered in the threads.
+	 */
 	kill(pid, SIGSTOP);
-	if (waitpid(pid, NULL, 0) < 0)
-		err(1, "Unexpected stop in waitpid");
-
+	for (;;) {
+		if (waitpid(pid, &status, 0) < 0)
+			err(1, "Unexpected error in waitpid");
+		sig = WIFSTOPPED(status) ? WSTOPSIG(status) : 0;
+		if (sig == SIGSTOP)
+			break;
+		if (sig == SIGTRAP)
+			sig = 0;
+		if (ptrace(PT_CONTINUE, pid, (caddr_t)1, sig) < 0)
+			err(1, "Can not continue for detach");
+	}	
+		
 	if (ptrace(PT_DETACH, pid, (caddr_t)1, 0) < 0)
 		err(1, "Can not detach the process");
 
diff --git a/usr.bin/truss/syscalls.c b/usr.bin/truss/syscalls.c
--- a/usr.bin/truss/syscalls.c
+++ b/usr.bin/truss/syscalls.c
@@ -1945,11 +1945,9 @@
 		fputs(strsig2(args[sc->offset]), fp);
 		break;
 	case Sigset: {
-		long sig;
 		sigset_t ss;
 		int i, first;
 
-		sig = args[sc->offset];
 		if (get_struct(pid, args[sc->offset], (void *)&ss,
 		    sizeof(ss)) == -1) {
 			print_pointer(fp, args[sc->offset]);