diff --git a/Refit.Tests/InterfaceStubGenerator.cs b/Refit.Tests/InterfaceStubGenerator.cs
index 25ecca9cf..1b6a62bac 100644
--- a/Refit.Tests/InterfaceStubGenerator.cs
+++ b/Refit.Tests/InterfaceStubGenerator.cs
@@ -123,7 +123,7 @@ public void GenerateTemplateInfoForInterfaceListSmokeTest()
                 .ToList();
 
             var result = fixture.GenerateTemplateInfoForInterfaceList(input);
-            Assert.Equal(11, result.ClassList.Count);
+            Assert.Equal(12, result.ClassList.Count);
         }
 
         [Fact]
diff --git a/Refit.Tests/RefitStubs.Net46.cs b/Refit.Tests/RefitStubs.Net46.cs
index 68e2ec8e4..fda73a626 100644
--- a/Refit.Tests/RefitStubs.Net46.cs
+++ b/Refit.Tests/RefitStubs.Net46.cs
@@ -1241,3 +1241,35 @@ public virtual Task<HttpResponseMessage> Get(int httpstatuscode)
         }
     }
 }
+
+namespace Refit.Tests
+{
+    using Refit.Tests.RefitInternalGenerated;
+
+    /// <inheritdoc />
+    [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+    [global::System.Diagnostics.DebuggerNonUserCode]
+    [Preserve]
+    [global::System.Reflection.Obfuscation(Exclude=true)]
+    partial class AutoGeneratedIValidApi : IValidApi
+    {
+        /// <inheritdoc />
+        public HttpClient Client { get; protected set; }
+        readonly IRequestBuilder requestBuilder;
+
+        /// <inheritdoc />
+        public AutoGeneratedIValidApi(HttpClient client, IRequestBuilder requestBuilder)
+        {
+            Client = client;
+            this.requestBuilder = requestBuilder;
+        }
+
+        /// <inheritdoc />
+        public virtual Task Get()
+        {
+            var arguments = new object[] {  };
+            var func = requestBuilder.BuildRestResultFuncForMethod("Get", new Type[] {  });
+            return (Task)func(Client, arguments);
+        }
+    }
+}
diff --git a/Refit.Tests/RefitStubs.NetCore2.cs b/Refit.Tests/RefitStubs.NetCore2.cs
index 68e2ec8e4..fda73a626 100644
--- a/Refit.Tests/RefitStubs.NetCore2.cs
+++ b/Refit.Tests/RefitStubs.NetCore2.cs
@@ -1241,3 +1241,35 @@ public virtual Task<HttpResponseMessage> Get(int httpstatuscode)
         }
     }
 }
+
+namespace Refit.Tests
+{
+    using Refit.Tests.RefitInternalGenerated;
+
+    /// <inheritdoc />
+    [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
+    [global::System.Diagnostics.DebuggerNonUserCode]
+    [Preserve]
+    [global::System.Reflection.Obfuscation(Exclude=true)]
+    partial class AutoGeneratedIValidApi : IValidApi
+    {
+        /// <inheritdoc />
+        public HttpClient Client { get; protected set; }
+        readonly IRequestBuilder requestBuilder;
+
+        /// <inheritdoc />
+        public AutoGeneratedIValidApi(HttpClient client, IRequestBuilder requestBuilder)
+        {
+            Client = client;
+            this.requestBuilder = requestBuilder;
+        }
+
+        /// <inheritdoc />
+        public virtual Task Get()
+        {
+            var arguments = new object[] {  };
+            var func = requestBuilder.BuildRestResultFuncForMethod("Get", new Type[] {  });
+            return (Task)func(Client, arguments);
+        }
+    }
+}
diff --git a/Refit.Tests/RestService.cs b/Refit.Tests/RestService.cs
index 2e5c7639a..710f8a250 100644
--- a/Refit.Tests/RestService.cs
+++ b/Refit.Tests/RestService.cs
@@ -139,6 +139,12 @@ public interface ITrimTrailingForwardSlashApi
         Task Get();
     }
 
+    public interface IValidApi
+    {
+        [Get("/someendpoint")]
+        Task Get();
+    }
+
     public class HttpBinGet
     {
         public Dictionary<string, object> Args { get; set; }
@@ -1206,5 +1212,53 @@ public void ShouldTrimTrailingForwardSlashFromBaseUrl()
 
             Assert.Equal(fixture.Client.BaseAddress.AbsoluteUri, expectedBaseAddress);
         }
+
+        [Fact]
+        public void ShouldThrowArgumentExceptionIfHostUrlIsNull()
+        {
+            try
+            {
+                RestService.For<IValidApi>(hostUrl: null);
+            }
+            catch (ArgumentException ex)
+            {
+                Assert.Equal("hostUrl", ex.ParamName);
+                return;
+            }
+
+            Assert.False(true, "Exception not thrown.");
+        }
+
+        [Fact]
+        public void ShouldThrowArgumentExceptionIfHostUrlIsEmpty()
+        {
+            try
+            {
+                RestService.For<IValidApi>(hostUrl: "");
+            }
+            catch (ArgumentException ex)
+            {
+                Assert.Equal("hostUrl", ex.ParamName);
+                return;
+            }
+
+            Assert.False(true, "Exception not thrown.");
+        }
+
+        [Fact]
+        public void ShouldThrowArgumentExceptionIfHostUrlIsWhitespace()
+        {
+            try
+            {
+                RestService.For<IValidApi>(hostUrl: " ");
+            }
+            catch (ArgumentException ex)
+            {
+                Assert.Equal("hostUrl", ex.ParamName);
+                return;
+            }
+
+            Assert.False(true, "Exception not thrown.");
+        }
     }
 }
diff --git a/Refit/RestService.cs b/Refit/RestService.cs
index fb5f3df28..d219b842a 100644
--- a/Refit/RestService.cs
+++ b/Refit/RestService.cs
@@ -34,6 +34,13 @@ public static T For<T>(HttpClient client, RefitSettings settings)
 
         public static T For<T>(string hostUrl, RefitSettings settings)
         {
+            if (string.IsNullOrWhiteSpace(hostUrl))
+            {
+                throw new ArgumentException(
+                    $"`{nameof(hostUrl)}` must not be null or whitespace.",
+                    nameof(hostUrl));
+            }
+
             // check to see if user provided custom auth token
             HttpMessageHandler innerHandler = null;
             if (settings != null)
@@ -49,7 +56,7 @@ public static T For<T>(string hostUrl, RefitSettings settings)
                 }
             }
 
-            var client = new HttpClient(innerHandler ?? new HttpClientHandler()) { BaseAddress = new Uri(hostUrl?.TrimEnd('/')) };
+            var client = new HttpClient(innerHandler ?? new HttpClientHandler()) { BaseAddress = new Uri(hostUrl.TrimEnd('/')) };
             return For<T>(client, settings);
         }