diff --git a/misc/ios/go_darwin_arm_exec.go b/misc/ios/go_darwin_arm_exec.go
index cc57adb584a..b49496cc106 100644
--- a/misc/ios/go_darwin_arm_exec.go
+++ b/misc/ios/go_darwin_arm_exec.go
@@ -100,7 +100,7 @@ func main() {
 	//
 	// The lock file is never deleted, to avoid concurrent locks on distinct
 	// files with the same path.
-	lockName := filepath.Join(os.TempDir(), "go_darwin_arm_exec.lock")
+	lockName := filepath.Join(os.TempDir(), "go_darwin_arm_exec-"+deviceID+".lock")
 	lock, err = os.OpenFile(lockName, os.O_CREATE|os.O_RDONLY, 0666)
 	if err != nil {
 		log.Fatal(err)
diff --git a/src/iostest.bash b/src/iostest.bash
index 595b6757440..00cc49ec7e6 100755
--- a/src/iostest.bash
+++ b/src/iostest.bash
@@ -32,11 +32,15 @@ if [ "$1" = "-restart" ]; then
 	# Reboot to make sure previous runs do not interfere with the current run.
 	# It is reasonably easy for a bad program leave an iOS device in an
 	# almost unusable state.
-	idevicediagnostics restart
+	IDEVARGS=
+	if [ -n "$GOIOS_DEVICE_ID" ]; then
+		IDEVARGS="-u $GOIOS_DEVICE_ID"
+	fi
+	idevicediagnostics $IDEVARGS restart
 	# Initial sleep to make sure we are restarting before we start polling.
 	sleep 30
 	# Poll until the device has restarted.
-	until idevicediagnostics diagnostics; do
+	until idevicediagnostics $IDEVARGS diagnostics; do
 		# TODO(crawshaw): replace with a test app using go_darwin_arm_exec.
 		echo "waiting for idevice to come online"
 		sleep 10