diff --git a/src/Flurl.Http/Configuration/DefaultJsonSerializer.cs b/src/Flurl.Http/Configuration/DefaultJsonSerializer.cs
index 580217cd..0bc346b3 100644
--- a/src/Flurl.Http/Configuration/DefaultJsonSerializer.cs
+++ b/src/Flurl.Http/Configuration/DefaultJsonSerializer.cs
@@ -35,6 +35,8 @@ public DefaultJsonSerializer(JsonSerializerOptions options = null) {
 		/// Deserializes the specified stream to an object of type T.
 		/// </summary>
 		/// <param name="stream">The stream to deserialize.</param>
-		public T Deserialize<T>(Stream stream) => stream.Length == 0 ? default : JsonSerializer.Deserialize<T>(stream, _options);
+		public T Deserialize<T>(Stream stream) => stream.CanSeek && stream.Length == 0
+			? default
+			: JsonSerializer.Deserialize<T>(stream, _options);
 	}
 }
\ No newline at end of file
diff --git a/src/Flurl.Http/Flurl.Http.csproj b/src/Flurl.Http/Flurl.Http.csproj
index 773828c1..a0104431 100644
--- a/src/Flurl.Http/Flurl.Http.csproj
+++ b/src/Flurl.Http/Flurl.Http.csproj
@@ -4,7 +4,7 @@
     <LangVersion>9.0</LangVersion>
     <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
     <PackageId>Flurl.Http</PackageId>
-    <Version>4.0.1</Version>
+    <Version>4.0.2</Version>
     <Authors>Todd Menier</Authors>
     <Description>A fluent, testable HTTP client library.</Description>
     <Copyright>Copyright (c) Todd Menier 2024.</Copyright>
diff --git a/src/Flurl.Http/FlurlHttp.cs b/src/Flurl.Http/FlurlHttp.cs
index 7c633c5d..bfd69cba 100644
--- a/src/Flurl.Http/FlurlHttp.cs
+++ b/src/Flurl.Http/FlurlHttp.cs
@@ -48,6 +48,6 @@ public static IFlurlClientBuilder ConfigureClientForUrl(string url) {
 		/// <summary>
 		/// Builds a cache key consisting of URL scheme, host, and port. This is the default client caching strategy.
 		/// </summary>
-		public static string BuildClientNameByHost(IFlurlRequest req) => $"{req.Url.Scheme}|{req.Url.Host}|{req.Url.Port}";
+		public static string BuildClientNameByHost(IFlurlRequest req) => $"{req.Url?.Scheme}|{req.Url?.Host}|{req.Url?.Port}";
 	}
 }
\ No newline at end of file
diff --git a/src/Flurl.Http/FlurlRequest.cs b/src/Flurl.Http/FlurlRequest.cs
index ca9762b4..c98e6649 100644
--- a/src/Flurl.Http/FlurlRequest.cs
+++ b/src/Flurl.Http/FlurlRequest.cs
@@ -115,6 +115,7 @@ public IFlurlClient Client {
 			set {
 				_client = value;
 				Settings.Parent = _client?.Settings;
+				SyncBaseUrl(_client, this);
 				SyncHeaders(_client, this);
 			}
 		}
@@ -163,6 +164,19 @@ internal static void SyncHeaders(IFlurlClient client, IFlurlRequest request) {
 			}
 		}
 
+		/// <summary>
+		/// Prepends client.BaseUrl to this.Url, but only if this.Url isn't already a valid, absolute URL.
+		/// </summary>
+		private static void SyncBaseUrl(IFlurlClient client, IFlurlRequest request) {
+			if (string.IsNullOrEmpty(client?.BaseUrl))
+				return;
+
+			if (request.Url == null)
+				request.Url = client.BaseUrl;
+			else if (!Url.IsValid(request.Url))
+				request.Url = Url.Combine(client.BaseUrl, request.Url);
+		}
+
 		private void ApplyCookieJar(CookieJar jar) {
 			_jar = jar;
 			if (jar == null)
diff --git a/test/Flurl.Test/Http/GlobalConfigTests.cs b/test/Flurl.Test/Http/GlobalConfigTests.cs
index fecd033b..73ffb61d 100644
--- a/test/Flurl.Test/Http/GlobalConfigTests.cs
+++ b/test/Flurl.Test/Http/GlobalConfigTests.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Threading.Tasks;
 using Flurl.Http;
+using Flurl.Http.Testing;
 using NUnit.Framework;
 
 namespace Flurl.Test.Http
@@ -74,5 +75,23 @@ public void can_configure_client_for_url() {
 			Assert.AreEqual(123, cli2.Settings.Timeout.Value.TotalSeconds);
 			Assert.AreNotEqual(123, cli3.Settings.Timeout.Value.TotalSeconds);
 		}
+
+		[Test] // #803
+		public async Task can_prepend_global_base_url() {
+			FlurlHttp.Clients.WithDefaults(builder =>
+				builder.ConfigureHttpClient(cli => cli.BaseAddress = new Uri("https://api.com")));
+
+			using var test = new HttpTest();
+
+			await "".GetAsync();
+			await "/path/1".GetAsync();
+			await "path/2".GetAsync();
+			await "https://other.com/path/3".GetAsync();
+
+			test.ShouldHaveCalled("https://api.com/").Times(1);
+			test.ShouldHaveCalled("https://api.com/path/1").Times(1);
+			test.ShouldHaveCalled("https://api.com/path/2").Times(1);
+			test.ShouldHaveCalled("https://other.com/path/3").Times(1);
+		}
 	}
 }
diff --git a/test/Flurl.Test/Http/RealHttpTests.cs b/test/Flurl.Test/Http/RealHttpTests.cs
index 8bfca19c..98763281 100644
--- a/test/Flurl.Test/Http/RealHttpTests.cs
+++ b/test/Flurl.Test/Http/RealHttpTests.cs
@@ -60,6 +60,19 @@ public async Task can_post_and_receive_json() {
 			Assert.AreEqual(2, result.json["b"].GetInt32());
 		}
 
+		[Test]
+		[TestCase(HttpCompletionOption.ResponseHeadersRead)]
+		[TestCase(HttpCompletionOption.ResponseContentRead)]
+		public async Task can_get_json_with_http_completion_option_headers(HttpCompletionOption completionOption)
+		{
+			var result = await "https://httpbin.org"
+				.AppendPathSegment("gzip")
+				.WithHeader("Accept-encoding", "gzip")
+				.GetJsonAsync<Dictionary<string, object>>(completionOption);
+
+			Assert.AreEqual(true, ((JsonElement)result["gzipped"]).GetBoolean());
+		}
+
 		[Test]
 		public async Task can_get_stream() {
 			using (var stream = await "https://www.google.com".GetStreamAsync())