diff --git a/cmds/portmaster-start/lock.go b/cmds/portmaster-start/lock.go
index 673844b3..68300214 100644
--- a/cmds/portmaster-start/lock.go
+++ b/cmds/portmaster-start/lock.go
@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"os/user"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -13,8 +14,22 @@ import (
 	processInfo "github.com/shirou/gopsutil/process"
 )
 
-func checkAndCreateInstanceLock(path, name string) (pid int32, err error) {
-	lockFilePath := filepath.Join(dataRoot.Path, path, fmt.Sprintf("%s-lock.pid", name))
+func checkAndCreateInstanceLock(path, name string, perUser bool) (pid int32, err error) {
+	var lockFilePath string
+	if perUser {
+		// Get user ID for per-user lock file.
+		var userID string
+		usr, err := user.Current()
+		if err != nil {
+			log.Printf("failed to get current user: %s\n", err)
+			userID = "no-user"
+		} else {
+			userID = usr.Uid
+		}
+		lockFilePath = filepath.Join(dataRoot.Path, path, fmt.Sprintf("%s-%s-lock.pid", name, userID))
+	} else {
+		lockFilePath = filepath.Join(dataRoot.Path, path, fmt.Sprintf("%s-lock.pid", name))
+	}
 
 	// read current pid file
 	data, err := ioutil.ReadFile(lockFilePath)
diff --git a/cmds/portmaster-start/run.go b/cmds/portmaster-start/run.go
index b37ba079..34c9129b 100644
--- a/cmds/portmaster-start/run.go
+++ b/cmds/portmaster-start/run.go
@@ -46,6 +46,7 @@ type Options struct {
 	Identifier        string // component identifier
 	ShortIdentifier   string // populated automatically
 	LockPathPrefix    string
+	LockPerUser       bool
 	PIDFile           bool
 	SuppressArgs      bool // do not use any args
 	AllowDownload     bool // allow download of component if it is not yet available
@@ -73,6 +74,7 @@ func init() {
 		{
 			Name:              "Portmaster Notifier",
 			Identifier:        "notifier/portmaster-notifier",
+			LockPerUser:       true,
 			AllowDownload:     false,
 			AllowHidingWindow: true,
 			PIDFile:           true,
@@ -162,7 +164,7 @@ func run(opts *Options, cmdArgs []string) (err error) {
 
 	// check for duplicate instances
 	if opts.PIDFile {
-		pid, err := checkAndCreateInstanceLock(opts.LockPathPrefix, opts.ShortIdentifier)
+		pid, err := checkAndCreateInstanceLock(opts.LockPathPrefix, opts.ShortIdentifier, opts.LockPerUser)
 		if err != nil {
 			return fmt.Errorf("failed to exec lock: %w", err)
 		}