diff --git a/lib/PuppeteerSharp.Tests/CookiesTests/CookiesTests.cs b/lib/PuppeteerSharp.Tests/CookiesTests/CookiesTests.cs
index a16a8a726..a7668d82a 100644
--- a/lib/PuppeteerSharp.Tests/CookiesTests/CookiesTests.cs
+++ b/lib/PuppeteerSharp.Tests/CookiesTests/CookiesTests.cs
@@ -77,6 +77,43 @@ public async Task ShouldProperlyReportLaxSameSiteCookie()
             Assert.That(cookies[0].SameSite, Is.EqualTo(SameSite.Lax));
         }
 
+        [Test, PuppeteerTest("cookies.spec", "Cookie specs Page.cookies", "should properly report \"Default\" sameSite cookie")]
+        public async Task ShouldProperlyReportDefaultSameSiteCookie()
+        {
+            await Page.GoToAsync(TestConstants.EmptyPage);
+            await Page.SetCookieAsync(new CookieParam
+            {
+                Name = "a",
+                Value = "b",
+                SameSite = SameSite.Default,
+            });
+            var cookies = await Page.GetCookiesAsync();
+            Assert.That(cookies, Has.Exactly(1).Items);
+            Assert.That(cookies[0].Name, Is.EqualTo("a"));
+
+            // Different browsers have different sameSite values for the "Default" sameSite.
+            Assert.That(
+                new SameSite?[] { SameSite.Default, SameSite.Lax, null },
+                Does.Contain(cookies[0].SameSite));
+        }
+
+        [Test, PuppeteerTest("cookies.spec", "Cookie specs Page.cookies", "should report \"Default\" sameSite cookie when not specified")]
+        public async Task ShouldReportDefaultSameSiteCookieWhenNotSpecified()
+        {
+            Server.SetRoute("/empty.html", context =>
+            {
+                context.Response.Headers["Set-Cookie"] = "a=b";
+                return Task.CompletedTask;
+            });
+            await Page.GoToAsync(TestConstants.EmptyPage);
+            var cookies = await Page.GetCookiesAsync();
+            Assert.That(cookies, Has.Exactly(1).Items);
+            if (!TestConstants.IsChrome && !PuppeteerTestAttribute.IsCdp)
+            {
+                Assert.That(cookies[0].SameSite, Is.EqualTo(SameSite.Default));
+            }
+        }
+
         [Test, PuppeteerTest("cookies.spec", "Cookie specs Page.cookies", "should get multiple cookies")]
         public async Task ShouldGetMultipleCookies()
         {
diff --git a/lib/PuppeteerSharp.Tests/CookiesTests/SetCookiesTests.cs b/lib/PuppeteerSharp.Tests/CookiesTests/SetCookiesTests.cs
index f653875ff..c1d2cfd9a 100644
--- a/lib/PuppeteerSharp.Tests/CookiesTests/SetCookiesTests.cs
+++ b/lib/PuppeteerSharp.Tests/CookiesTests/SetCookiesTests.cs
@@ -227,6 +227,22 @@ await page.SetCookieAsync(new CookieParam
             Assert.That(cookie.PartitionKey, Is.EqualTo(key));
         }
 
+        [Test, PuppeteerTest("cookies.spec", "Cookie specs Page.setCookie", "should be able to delete \"Default\" sameSite cookie")]
+        public async Task ShouldBeAbleToDeleteDefaultSameSiteCookie()
+        {
+            await Page.GoToAsync(TestConstants.EmptyPage);
+            await Page.SetCookieAsync(new CookieParam
+            {
+                Name = "a",
+                Value = "b",
+                SameSite = SameSite.Default,
+            });
+            var cookies = await Page.GetCookiesAsync();
+            Assert.That(cookies.Any(c => c.Name == "a"), Is.True);
+            await Page.DeleteCookieAsync(cookies);
+            Assert.That(await Page.GetCookiesAsync(), Is.Empty);
+        }
+
         [Test, PuppeteerTest("cookies.spec", "Cookie specs Page.setCookie", "should not set a cookie on a blank page")]
         public async Task ShouldNotSetACookieOnABlankPage()
         {
diff --git a/lib/PuppeteerSharp/Bidi/BidiCookieHelper.cs b/lib/PuppeteerSharp/Bidi/BidiCookieHelper.cs
index 1521e7bdc..d7d1e93c4 100644
--- a/lib/PuppeteerSharp/Bidi/BidiCookieHelper.cs
+++ b/lib/PuppeteerSharp/Bidi/BidiCookieHelper.cs
@@ -178,7 +178,8 @@ private static SameSite ConvertSameSiteBidiToPuppeteer(CookieSameSiteValue sameS
         {
             CookieSameSiteValue.Strict => SameSite.Strict,
             CookieSameSiteValue.Lax => SameSite.Lax,
-            _ => SameSite.None,
+            CookieSameSiteValue.None => SameSite.None,
+            _ => SameSite.Default,
         };
     }
 
@@ -189,7 +190,7 @@ private static SameSite ConvertSameSiteBidiToPuppeteer(CookieSameSiteValue sameS
             SameSite.Strict => CookieSameSiteValue.Strict,
             SameSite.Lax => CookieSameSiteValue.Lax,
             SameSite.None => CookieSameSiteValue.None,
-            _ => null,
+            _ => CookieSameSiteValue.Default,
         };
     }
 
diff --git a/lib/PuppeteerSharp/Cdp/CdpPage.cs b/lib/PuppeteerSharp/Cdp/CdpPage.cs
index 3f88a3e91..057084209 100644
--- a/lib/PuppeteerSharp/Cdp/CdpPage.cs
+++ b/lib/PuppeteerSharp/Cdp/CdpPage.cs
@@ -214,6 +214,11 @@ public override async Task SetCookieAsync(params CookieParam[] cookies)
 
         if (cookies.Length > 0)
         {
+            foreach (var cookie in cookies)
+            {
+                cookie.SameSite = ConvertSameSiteForCdp(cookie.SameSite);
+            }
+
             await PrimaryTargetClient
                 .SendAsync("Network.setCookies", new NetworkSetCookiesRequest { Cookies = cookies, })
                 .ConfigureAwait(false);
@@ -987,6 +992,19 @@ protected override async Task<string> PerformScreenshotAsync(ScreenshotType type
         _ => null,
     };
 
+    /// <summary>
+    /// Converts a PuppeteerSharp SameSite value to a CDP-compatible value.
+    /// CDP does not support "Default", so we map it to null (omitted).
+    /// </summary>
+    private static SameSite? ConvertSameSiteForCdp(SameSite? sameSite)
+    {
+        return sameSite switch
+        {
+            SameSite.Strict or SameSite.Lax or SameSite.None => sameSite,
+            _ => null,
+        };
+    }
+
     private void SetupPrimaryTargetListeners()
     {
         PrimaryTargetClient.Ready += OnAttachedToTarget;
diff --git a/lib/PuppeteerSharp/SameSite.cs b/lib/PuppeteerSharp/SameSite.cs
index ffd818424..d8018e196 100644
--- a/lib/PuppeteerSharp/SameSite.cs
+++ b/lib/PuppeteerSharp/SameSite.cs
@@ -29,5 +29,10 @@ public enum SameSite
         /// Extended.
         /// </summary>
         Extended,
+
+        /// <summary>
+        /// Default. The browser applies its default SameSite behavior.
+        /// </summary>
+        Default,
     }
 }