diff --git a/diskwriter/diskwriter.go b/diskwriter/diskwriter.go
index 02233b4..8e0a240 100644
--- a/diskwriter/diskwriter.go
+++ b/diskwriter/diskwriter.go
@@ -264,7 +264,7 @@ func openDiskFile(directory, username, extension string) (*os.File, error) {
 		)
 		if err == nil {
 			return f, nil
-		} else if !os.IsExist(err) {
+		} else if !errors.Is(err, os.ErrExist) {
 			return nil, err
 		}
 	}
diff --git a/group/description.go b/group/description.go
index 53671d6..0d5a080 100644
--- a/group/description.go
+++ b/group/description.go
@@ -232,7 +232,7 @@ func getDescriptionFile[T any](name string, allowSubgroups bool, get func(string
 			Directory, path.Clean("/"+name)+".json",
 		)
 		r, err := get(fileName)
-		if !os.IsNotExist(err) {
+		if !errors.Is(err, os.ErrNotExist) {
 			return r, fileName, isSubgroup, err
 		}
 		if !allowSubgroups {
@@ -348,7 +348,7 @@ func UpdateDescription(name, etag string, desc *Description) error {
 	if err == nil {
 		oldetag = makeETag(old.fileSize, old.modTime)
 		filename = old.FileName
-	} else if os.IsNotExist(err) {
+	} else if errors.Is(err, os.ErrNotExist) {
 		old = nil
 		filename = filepath.Join(
 			Directory, path.Clean("/"+name)+".json",
diff --git a/group/group.go b/group/group.go
index e92a990..2e899f9 100644
--- a/group/group.go
+++ b/group/group.go
@@ -474,7 +474,7 @@ func add(name string, desc *Description) (*Group, []Client, error) {
 	} else if !descriptionUnchanged(name, g.description) {
 		desc, err = readDescription(name, true)
 		if err != nil {
-			if !os.IsNotExist(err) {
+			if !errors.Is(err, os.ErrNotExist) {
 				log.Printf("Reading group %v: %v", name, err)
 			}
 			deleteUnlocked(g)
@@ -886,7 +886,7 @@ func GetConfiguration() (*Configuration, error) {
 	filename := filepath.Join(DataDirectory, "config.json")
 	fi, err := os.Stat(filename)
 	if err != nil {
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			if !configuration.configuration.Zero() {
 				configuration.configuration = &Configuration{}
 			}
diff --git a/ice/ice.go b/ice/ice.go
index 9942781..e299b54 100644
--- a/ice/ice.go
+++ b/ice/ice.go
@@ -95,7 +95,7 @@ func Update() *configuration {
 		found = true
 		file, err := os.Open(ICEFilename)
 		if err != nil {
-			if !os.IsNotExist(err) {
+			if !errors.Is(err, os.ErrNotExist) {
 				log.Printf("Open %v: %v", ICEFilename, err)
 			} else {
 				found = false
diff --git a/rtpconn/webclient.go b/rtpconn/webclient.go
index 5d6aae8..178509c 100644
--- a/rtpconn/webclient.go
+++ b/rtpconn/webclient.go
@@ -1299,7 +1299,7 @@ func leaveGroup(c *webClient) {
 
 func closeDownConn(c *webClient, id string, message string) error {
 	err := delDownConn(c, id)
-	if err != nil && !os.IsNotExist(err) {
+	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		log.Printf("Close down connection: %v", err)
 	}
 	err = c.write(clientMessage{
@@ -1413,7 +1413,7 @@ func handleClientMessage(c *webClient, m clientMessage) error {
 		if err != nil {
 			var e, s string
 			var autherr *group.NotAuthorisedError
-			if os.IsNotExist(err) {
+			if errors.Is(err, os.ErrNotExist) {
 				s = "group does not exist"
 			} else if errors.Is(err, group.ErrAnonymousNotAuthorised) {
 				s = "please choose a username"
diff --git a/token/stateful.go b/token/stateful.go
index 45f1813..1d0fb4b 100644
--- a/token/stateful.go
+++ b/token/stateful.go
@@ -62,7 +62,7 @@ func getStateful(token string) (*Stateful, error) {
 	defer tokens.mu.Unlock()
 	err := tokens.load()
 	if err != nil {
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			return nil, nil
 		}
 		return nil, err
@@ -109,7 +109,7 @@ func (state *state) load() error {
 		state.modTime = time.Time{}
 		state.fileSize = 0
 		state.tokens = nil
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			return nil
 		}
 		return err
@@ -125,7 +125,7 @@ func (state *state) load() error {
 		state.modTime = time.Time{}
 		state.fileSize = 0
 		state.tokens = nil
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			return nil
 		}
 		return err
@@ -153,7 +153,7 @@ func (state *state) load() error {
 		state.modTime = time.Time{}
 		state.fileSize = 0
 		state.tokens = nil
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			return nil
 		}
 		return err
@@ -262,7 +262,7 @@ func (state *state) extend(group, token string, expires time.Time) (*Stateful, e
 func (state *state) rewrite() error {
 	if state.tokens == nil || len(state.tokens) == 0 {
 		err := os.Remove(state.filename)
-		if err == nil || os.IsNotExist(err) {
+		if err == nil || errors.Is(err, os.ErrNotExist) {
 			return nil
 		}
 		return err
diff --git a/token/stateful_test.go b/token/stateful_test.go
index 9a88179..c98873c 100644
--- a/token/stateful_test.go
+++ b/token/stateful_test.go
@@ -2,6 +2,7 @@ package token
 
 import (
 	"encoding/json"
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -294,7 +295,7 @@ func TestTokenStorage(t *testing.T) {
 	}
 
 	_, err = os.Stat(s.filename)
-	if !os.IsNotExist(err) {
+	if !errors.Is(err, os.ErrNotExist) {
 		t.Errorf("existence check: %v", err)
 	}
 }
diff --git a/webserver/api.go b/webserver/api.go
index 0d0ba0e..b497230 100644
--- a/webserver/api.go
+++ b/webserver/api.go
@@ -5,6 +5,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -170,7 +171,7 @@ func apiGroupHandler(w http.ResponseWriter, r *http.Request, pth string) {
 		return
 	} else if r.Method == "PUT" {
 		etag, err := group.GetDescriptionTag(g)
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			err = nil
 			etag = ""
 		} else if err != nil {
@@ -299,7 +300,7 @@ func usersHandler(w http.ResponseWriter, r *http.Request, g, pth string) {
 		return
 	} else if r.Method == "PUT" {
 		etag, err := group.GetUserTag(g, username)
-		if os.IsNotExist(err) {
+		if errors.Is(err, os.ErrNotExist) {
 			etag = ""
 			err = nil
 		} else if err != nil {
diff --git a/webserver/api_test.go b/webserver/api_test.go
index 70ee9fb..a4d18e3 100644
--- a/webserver/api_test.go
+++ b/webserver/api_test.go
@@ -291,7 +291,7 @@ func TestApi(t *testing.T) {
 	}
 
 	_, err = group.GetDescription("test")
-	if !os.IsNotExist(err) {
+	if !errors.Is(err, os.ErrNotExist) {
 		t.Errorf("Group exists after delete")
 	}
 }
diff --git a/webserver/webserver.go b/webserver/webserver.go
index 7e7ace7..a8914ec 100644
--- a/webserver/webserver.go
+++ b/webserver/webserver.go
@@ -120,7 +120,7 @@ func notFound(w http.ResponseWriter) {
 var ErrIsDirectory = errors.New("is a directory")
 
 func httpError(w http.ResponseWriter, err error) {
-	if os.IsNotExist(err) {
+	if errors.Is(err, os.ErrNotExist) {
 		notFound(w)
 		return
 	}
@@ -235,7 +235,7 @@ func (fh *fileHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		ff, err := fh.root.Open(index)
 		if err != nil {
 			// return 403 if index.html doesn't exist
-			if os.IsNotExist(err) {
+			if errors.Is(err, os.ErrNotExist) {
 				http.Error(w, "Forbidden", http.StatusForbidden)
 				return
 			}