diff --git a/go_backend/extension_cookie_jar_test.go b/go_backend/extension_cookie_jar_test.go
new file mode 100644
index 00000000..3d3e54bd
--- /dev/null
+++ b/go_backend/extension_cookie_jar_test.go
@@ -0,0 +1,57 @@
+package gobackend
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+	"time"
+)
+
+func TestSimpleCookieJarReplacesAndExpiresCookies(t *testing.T) {
+	jar, err := newSimpleCookieJar()
+	if err != nil {
+		t.Fatalf("newSimpleCookieJar: %v", err)
+	}
+	u, _ := url.Parse("https://api.example.com/path")
+
+	jar.SetCookies(u, []*http.Cookie{{Name: "session", Value: "old", Path: "/"}})
+	jar.SetCookies(u, []*http.Cookie{{Name: "session", Value: "new", Path: "/"}})
+	cookies := jar.Cookies(u)
+	if len(cookies) != 1 || cookies[0].Value != "new" {
+		t.Fatalf("replacement cookies = %#v", cookies)
+	}
+
+	jar.SetCookies(u, []*http.Cookie{{
+		Name:    "session",
+		Value:   "expired",
+		Path:    "/",
+		Expires: time.Now().Add(-time.Hour),
+		MaxAge:  -1,
+	}})
+	if cookies := jar.Cookies(u); len(cookies) != 0 {
+		t.Fatalf("expired cookies = %#v", cookies)
+	}
+}
+
+func TestSimpleCookieJarClearAndScope(t *testing.T) {
+	jar, err := newSimpleCookieJar()
+	if err != nil {
+		t.Fatalf("newSimpleCookieJar: %v", err)
+	}
+	apiURL, _ := url.Parse("https://api.example.com/private/resource")
+	otherURL, _ := url.Parse("https://other.example.com/private/resource")
+	publicURL, _ := url.Parse("https://api.example.com/public")
+
+	jar.SetCookies(apiURL, []*http.Cookie{{Name: "session", Value: "value", Path: "/private"}})
+	if len(jar.Cookies(apiURL)) != 1 {
+		t.Fatal("expected cookie for matching host and path")
+	}
+	if len(jar.Cookies(otherURL)) != 0 || len(jar.Cookies(publicURL)) != 0 {
+		t.Fatal("cookie escaped its host or path scope")
+	}
+
+	jar.Clear()
+	if len(jar.Cookies(apiURL)) != 0 {
+		t.Fatal("Clear retained cookies")
+	}
+}
diff --git a/go_backend/extension_runtime.go b/go_backend/extension_runtime.go
index d3f11dc1..52d6f78b 100644
--- a/go_backend/extension_runtime.go
+++ b/go_backend/extension_runtime.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/http"
+	"net/http/cookiejar"
 	"net/url"
 	"slices"
 	"strconv"
@@ -494,27 +495,36 @@ func isPrivateIPAddr(ip net.IP) bool {
 }
 
 type simpleCookieJar struct {
-	cookies map[string][]*http.Cookie
-	mu      sync.RWMutex
+	mu  sync.RWMutex
+	jar *cookiejar.Jar
 }
 
 func newSimpleCookieJar() (*simpleCookieJar, error) {
-	return &simpleCookieJar{
-		cookies: make(map[string][]*http.Cookie),
-	}, nil
+	jar, err := cookiejar.New(nil)
+	if err != nil {
+		return nil, err
+	}
+	return &simpleCookieJar{jar: jar}, nil
 }
 
 func (j *simpleCookieJar) SetCookies(u *url.URL, cookies []*http.Cookie) {
-	j.mu.Lock()
-	defer j.mu.Unlock()
-	key := u.Host
-	j.cookies[key] = append(j.cookies[key], cookies...)
+	j.mu.RLock()
+	defer j.mu.RUnlock()
+	j.jar.SetCookies(u, cookies)
 }
 
 func (j *simpleCookieJar) Cookies(u *url.URL) []*http.Cookie {
 	j.mu.RLock()
 	defer j.mu.RUnlock()
-	return j.cookies[u.Host]
+	return j.jar.Cookies(u)
+
+}
+
+func (j *simpleCookieJar) Clear() {
+	jar, _ := cookiejar.New(nil)
+	j.mu.Lock()
+	j.jar = jar
+	j.mu.Unlock()
 }
 
 func (r *extensionRuntime) SetSettings(settings map[string]any) {
diff --git a/go_backend/extension_runtime_http.go b/go_backend/extension_runtime_http.go
index c4d1118a..988f0eba 100644
--- a/go_backend/extension_runtime_http.go
+++ b/go_backend/extension_runtime_http.go
@@ -292,9 +292,7 @@ func (r *extensionRuntime) httpMethodShortcut(method string, call goja.FunctionC
 
 func (r *extensionRuntime) httpClearCookies(call goja.FunctionCall) goja.Value {
 	if jar, ok := r.cookieJar.(*simpleCookieJar); ok {
-		jar.mu.Lock()
-		jar.cookies = make(map[string][]*http.Cookie)
-		jar.mu.Unlock()
+		jar.Clear()
 		GoLog("[Extension:%s] Cookies cleared\n", r.extensionID)
 		return r.vm.ToValue(true)
 	}