diff --git a/Refit-Tests/RequestBuilder.cs b/Refit-Tests/RequestBuilder.cs
index af4d06730..3da09b2dc 100644
--- a/Refit-Tests/RequestBuilder.cs
+++ b/Refit-Tests/RequestBuilder.cs
@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using System.Net.Http;
 using System.Collections.Generic;
 using System.Linq;
@@ -228,6 +229,12 @@ public interface IDummyHttpApi
         Task FetchSomeStuffWithVoid();
 
         string SomeOtherMethod();
+
+        [Put("/foo/bar/{id}")]
+        Task PutSomeContentWithAuthorization(int id, [Body] object content, [Header("Authorization")] string authorization);
+
+        [Put("/foo/bar/{id}")]
+        Task<string> PutSomeStuffWithDynamicContentType(int id, [Body] string content, [Header("Content-Type")] string contentType);
     }
 
     public class TestHttpMessageHandler : HttpMessageHandler
@@ -423,5 +430,28 @@ public void HttpClientShouldNotPrefixEmptyAbsolutePathToTheRequestUri()
 
             Assert.AreEqual("http://api/foo/bar/42", testHttpMessageHandler.RequestMessage.RequestUri.ToString());            
         }
+
+        [Test]
+        public void DontBlowUpWithDynamicAuthorizationHeaderAndContent() 
+        {
+            var fixture = new RequestBuilderImplementation(typeof(IDummyHttpApi));
+            var factory = fixture.BuildRequestFactoryForMethod("PutSomeContentWithAuthorization");
+            var output = factory(new object[] { 7, new { Octocat = "Dunetocat" }, "Basic RnVjayB5ZWFoOmhlYWRlcnMh" });
+
+            Assert.IsNotNull(output.Headers.Authorization, "Headers include Authorization header");
+            Assert.AreEqual("RnVjayB5ZWFoOmhlYWRlcnMh", output.Headers.Authorization.Parameter);
+        }
+
+        [Test]
+        public void SuchFlexibleContentTypeWow()
+        {
+            var fixture = new RequestBuilderImplementation(typeof(IDummyHttpApi));
+            var factory = fixture.BuildRequestFactoryForMethod("PutSomeStuffWithDynamicContentType");
+            var output = factory(new object[] { 7, "such \"refit\" is \"amaze\" wow", "text/dson" });
+
+            Assert.IsNotNull(output.Content, "Request has content");
+            Assert.IsNotNull(output.Content.Headers.ContentType, "Headers include Content-Type header");
+            Assert.AreEqual("text/dson", output.Content.Headers.ContentType.MediaType, "Content-Type header has the expected value");
+        }
     }
 }
\ No newline at end of file
diff --git a/Refit/RequestBuilderImplementation.cs b/Refit/RequestBuilderImplementation.cs
index ebc294473..23cd46a13 100644
--- a/Refit/RequestBuilderImplementation.cs
+++ b/Refit/RequestBuilderImplementation.cs
@@ -122,10 +122,14 @@ public Func<object[], HttpRequestMessage> BuildRequestFactoryForMethod(string me
         void setHeader(HttpRequestMessage request, string name, object value) 
         {
             // Clear any existing version of this header we may have set, because
-            // we want to allow removal/redefinition of headers.
-            request.Headers.Remove(name);
+            // we want to allow removal/redefinition of headers. 
 
-            if (request.Content != null) {
+            // NB: We have to enumerate the header names to check existence because 
+            // Contains throws if it's the wrong header type for the collection.
+            if (request.Headers.Any(x => x.Key == name)) {
+                request.Headers.Remove(name);
+            }
+            if (request.Content != null && request.Content.Headers.Any(x => x.Key == name)) {
                 request.Content.Headers.Remove(name);
             }