diff --git a/RestSharp.Tests/RestRequestTests.cs b/RestSharp.Tests/RestRequestTests.cs
index 2e9342dfe..b296b7276 100644
--- a/RestSharp.Tests/RestRequestTests.cs
+++ b/RestSharp.Tests/RestRequestTests.cs
@@ -1,9 +1,11 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
 using Xunit;
 using System.Globalization;
+using Xunit.Extensions;
 
 namespace RestSharp.Tests {
 	public class RestRequestTests {
@@ -17,5 +19,54 @@ public void Can_Add_Object_With_IntegerArray_property() {
 			var request = new RestRequest();
 			request.AddObject(new { Items = new int[] { 2, 3, 4 } });
 		}
+
+		[Fact]
+		public void Cannot_Set_Empty_Host_Header()
+		{
+			var request = new RestRequest();
+
+			var exception = Assert.Throws<ArgumentException>(() => request.AddHeader("Host", string.Empty));
+			Assert.Equal("value", exception.ParamName);
+		}
+
+		[Theory]
+		[InlineData("http://localhost")]
+		[InlineData("hostname 1234")]
+		[InlineData("-leading.hyphen.not.allowed")]
+		[InlineData("bad:port")]
+		[InlineData(" no.leading.white-space")]
+		[InlineData("no.trailing.white-space ")]
+		[InlineData(".leading.dot.not.allowed")]
+		[InlineData("double.dots..not.allowed")]
+		[InlineData(".")]
+		[InlineData(".:2345")]
+		[InlineData(":5678")]
+		public void Cannot_Set_Invalid_Host_Header(string value)
+		{
+			var request = new RestRequest();
+
+			var exception = Assert.Throws<ArgumentException>(() => request.AddHeader("Host", value));
+			Assert.Equal("value", exception.ParamName);
+		}
+
+		[Theory]
+		[InlineData("localhost")]
+		[InlineData("localhost:1234")]
+		[InlineData("host.local")]
+		[InlineData("anotherhost.local:2345")]
+		[InlineData("www.w3.org")]
+		[InlineData("www.w3.org:3456")]
+		[InlineData("8.8.8.8")]
+		[InlineData("a.1.b.2")]
+		[InlineData("10.20.30.40:1234")]
+		[InlineData("0host")]
+		[InlineData("hypenated-hostname")]
+		[InlineData("multi--hyphens")]
+		public void Can_Set_Valid_Host_Header(string value)
+		{
+			var request = new RestRequest();
+
+			Assert.DoesNotThrow(() => request.AddHeader("Host", value));
+		}
 	}
 }
diff --git a/RestSharp/RestRequest.cs b/RestSharp/RestRequest.cs
index 2cbf2ee8b..6c328c6b9 100644
--- a/RestSharp/RestRequest.cs
+++ b/RestSharp/RestRequest.cs
@@ -19,6 +19,7 @@
 using System.IO;
 using System.Linq;
 using System.Net;
+using System.Text.RegularExpressions;
 using RestSharp.Extensions;
 using RestSharp.Serializers;
 
@@ -356,6 +357,12 @@ public IRestRequest AddParameter (string name, object value, ParameterType type)
 		/// <returns></returns>
 		public IRestRequest AddHeader (string name, string value)
 		{
+			const string portSplit = @":\d+";
+			Func<string, bool> invalidHost = host => Uri.CheckHostName(Regex.Split(host, portSplit)[0]) == UriHostNameType.Unknown;
+			if (name == "Host" && invalidHost(value))
+			{
+				throw new ArgumentException("The specified value is not a valid Host header string.", "value");
+			}
 			return AddParameter(name, value, ParameterType.HttpHeader);
 		}