diff --git a/CHANGELOG.md b/CHANGELOG.md
index b1bcffaa..b5be947b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,30 @@
 # Changelog
 
+## [2.6.0](https://github.com/Workvia/w_transport/compare/2.5.1...2.6.0)
+_TBD_
+
+- **Improvement:** the content-type for HTTP requests can now be set manually.
+
+    ```dart
+    var request = new Request()
+      ..uri = Uri.parse('/example')
+      ..contentType =
+          new MediaType('application', 'x-custom', {'charset': UTF8.name});
+    ```
+
+  - The content-type still has a default value based on the type of request
+    (`Request` - text/plain, `JsonRequest` - application/json, etc.).
+
+  - The content-type's charset parameter will still be updated automatically
+    when you set the `encoding`, **but once you manually set `contentType`, this
+    behavior will stop.** In other words, we are assuming that if you set
+    `contentType` manually, you are intentionally overriding the defaults and
+    are taking responsibility of setting the `charset` parameter appropriately.
+
+- **Bug Fix:** the `StreamedRequest` now properly verifies that the request has
+  not been sent when setting `contentType`. It will now throw a `StateError`
+  like the rest of the request types.
+
 ## [2.5.0](https://github.com/Workiva/w_transport/compare/2.4.0...2.5.0)
 _June 15, 2015_
 
diff --git a/lib/src/http/common/multipart_request.dart b/lib/src/http/common/multipart_request.dart
index 9c978a67..6959ef7e 100644
--- a/lib/src/http/common/multipart_request.dart
+++ b/lib/src/http/common/multipart_request.dart
@@ -112,6 +112,12 @@ abstract class CommonMultipartRequest extends CommonRequest
         'The content-length of a multipart request cannot be set manually.');
   }
 
+  @override
+  set contentType(MediaType contentType) {
+    throw new UnsupportedError(
+        'The content-type of a multipart request cannot be set manually.');
+  }
+
   @override
   MediaType get defaultContentType =>
       new MediaType('multipart', 'form-data', {'boundary': boundary});
@@ -119,7 +125,8 @@ abstract class CommonMultipartRequest extends CommonRequest
   @override
   set encoding(Encoding encoding) {
     throw new UnsupportedError(
-        'A multipart request has many individually-encoded parts. An encoding cannot be set for the entire request.');
+        'A multipart request has many individually-encoded parts. An encoding '
+        'cannot be set for the entire request.');
   }
 
   Map<String, String> get fields =>
diff --git a/lib/src/http/common/request.dart b/lib/src/http/common/request.dart
index 1fd9d453..f2895c8a 100644
--- a/lib/src/http/common/request.dart
+++ b/lib/src/http/common/request.dart
@@ -107,6 +107,11 @@ abstract class CommonRequest extends Object
   /// Content-type of this request.
   MediaType _contentType;
 
+  /// Whether or not the content-type was set manually. If `false`, the
+  /// content-type will continue to be updated automatically when the [encoding]
+  /// is set/changed. If `true`, the content-type will be left alone.
+  bool _contentTypeSetManually = false;
+
   /// Completer that should complete when the request has finished (successful
   /// or otherwise).
   Completer<Null> _done = new Completer();
@@ -155,12 +160,16 @@ abstract class CommonRequest extends Object
     return _contentType;
   }
 
-  /// By default, the content-type cannot be set manually because it's set
-  /// automatically based on the type of request. Streamed requests will be the
-  /// exception to this rule because the body is not known in advance.
+  /// Manually set the content-type for this request.
+  ///
+  /// NOTE: By default, the content-type will be set automatically based on the
+  /// request type and the [encoding]. Once you set the content-type manually,
+  /// we assume you are intentionally overriding this behavior and the
+  /// content-type will no longer be updated when [encoding] changes.
   set contentType(MediaType contentType) {
-    throw new UnsupportedError(
-        'The content-type is set automatically when the request body and type is known in advance.');
+    verifyUnsent();
+    _contentTypeSetManually = true;
+    updateContentType(contentType);
   }
 
   /// Set the content-type of this request. Used to update the charset
@@ -189,8 +198,10 @@ abstract class CommonRequest extends Object
   set encoding(Encoding encoding) {
     verifyUnsent();
     _encoding = encoding;
-    updateContentType(
-        contentType.change(parameters: {'charset': encoding.name}));
+    if (!_contentTypeSetManually) {
+      updateContentType(
+          contentType.change(parameters: {'charset': encoding.name}));
+    }
   }
 
   /// Get the request headers to be sent with this HTTP request.
diff --git a/lib/src/http/common/streamed_request.dart b/lib/src/http/common/streamed_request.dart
index 29744dd1..2076b89c 100644
--- a/lib/src/http/common/streamed_request.dart
+++ b/lib/src/http/common/streamed_request.dart
@@ -49,11 +49,6 @@ abstract class CommonStreamedRequest extends CommonRequest
     _contentLength = value;
   }
 
-  @override
-  set contentType(MediaType contentType) {
-    updateContentType(contentType);
-  }
-
   @override
   MediaType get defaultContentType =>
       new MediaType('text', 'plain', {'charset': encoding.name});
diff --git a/test/integration/http/form_request/suite.dart b/test/integration/http/form_request/suite.dart
index 875f5163..dc9f822c 100644
--- a/test/integration/http/form_request/suite.dart
+++ b/test/integration/http/form_request/suite.dart
@@ -59,6 +59,18 @@ void runFormRequestSuite() {
       expect(contentType.mimeType, equals('application/x-www-form-urlencoded'));
     });
 
+    test('content-type should be overridable', () async {
+      var contentType = new MediaType('application', 'x-custom');
+      FormRequest request = new FormRequest()
+        ..uri = IntegrationPaths.reflectEndpointUri
+        ..fields['field'] = 'value'
+        ..contentType = contentType;
+      Response response = await request.post();
+      var reflectedContentType = new MediaType.parse(
+          response.body.asJson()['headers']['content-type']);
+      expect(reflectedContentType.mimeType, equals(contentType.mimeType));
+    });
+
     test('UTF8', () async {
       FormRequest request = new FormRequest()
         ..uri = IntegrationPaths.echoEndpointUri
diff --git a/test/integration/http/json_request/suite.dart b/test/integration/http/json_request/suite.dart
index 5de7d9ae..f3a36694 100644
--- a/test/integration/http/json_request/suite.dart
+++ b/test/integration/http/json_request/suite.dart
@@ -54,6 +54,18 @@ void runJsonRequestSuite() {
       expect(contentType.mimeType, equals('application/json'));
     });
 
+    test('content-type should be overridable', () async {
+      var contentType = new MediaType('application', 'x-custom');
+      JsonRequest request = new JsonRequest()
+        ..uri = IntegrationPaths.reflectEndpointUri
+        ..body = {'field1': 'value1', 'field2': 'value2'}
+        ..contentType = contentType;
+      Response response = await request.post();
+      var reflectedContentType = new MediaType.parse(
+          response.body.asJson()['headers']['content-type']);
+      expect(reflectedContentType.mimeType, equals(contentType.mimeType));
+    });
+
     test('UTF8', () async {
       JsonRequest request = new JsonRequest()
         ..uri = IntegrationPaths.echoEndpointUri
diff --git a/test/integration/http/plain_text_request/suite.dart b/test/integration/http/plain_text_request/suite.dart
index fa679999..5942ec85 100644
--- a/test/integration/http/plain_text_request/suite.dart
+++ b/test/integration/http/plain_text_request/suite.dart
@@ -54,6 +54,18 @@ void runPlainTextRequestSuite() {
       expect(contentType.mimeType, equals('text/plain'));
     });
 
+    test('content-type should be overridable', () async {
+      var contentType = new MediaType('application', 'x-custom');
+      Request request = new Request()
+        ..uri = IntegrationPaths.reflectEndpointUri
+        ..body = 'data'
+        ..contentType = contentType;
+      Response response = await request.post();
+      var reflectedContentType = new MediaType.parse(
+          response.body.asJson()['headers']['content-type']);
+      expect(reflectedContentType.mimeType, equals(contentType.mimeType));
+    });
+
     test('UTF8', () async {
       Request request = new Request()
         ..uri = IntegrationPaths.echoEndpointUri
diff --git a/test/integration/http/streamed_request/suite.dart b/test/integration/http/streamed_request/suite.dart
index 89873423..c76661a3 100644
--- a/test/integration/http/streamed_request/suite.dart
+++ b/test/integration/http/streamed_request/suite.dart
@@ -69,6 +69,19 @@ void runStreamedRequestSuite() {
       expect(contentType.mimeType, equals('text/plain'));
     });
 
+    test('content-type should be overridable', () async {
+      var contentType = new MediaType('application', 'x-custom');
+      StreamedRequest request = new StreamedRequest()
+        ..uri = IntegrationPaths.reflectEndpointUri
+        ..body = new Stream.fromIterable([])
+        ..contentLength = 0
+        ..contentType = contentType;
+      Response response = await request.post();
+      var reflectedContentType = new MediaType.parse(
+          response.body.asJson()['headers']['content-type']);
+      expect(reflectedContentType.mimeType, equals(contentType.mimeType));
+    });
+
     test('UTF8', () async {
       StreamedRequest request = new StreamedRequest()
         ..uri = IntegrationPaths.echoEndpointUri
diff --git a/test/unit/http/form_request_test.dart b/test/unit/http/form_request_test.dart
index c81c780f..d9316062 100644
--- a/test/unit/http/form_request_test.dart
+++ b/test/unit/http/form_request_test.dart
@@ -35,11 +35,6 @@ void main() {
         configureWTransportForTest();
       });
 
-      test('content-type cannot be set manually', () {
-        FormRequest request = new FormRequest();
-        expect(() => request.contentType = null, throwsUnsupportedError);
-      });
-
       test('setting fields defaults to empty map if null', () {
         FormRequest request = new FormRequest()..fields = null;
         expect(request.fields, equals({}));
@@ -111,6 +106,33 @@ void main() {
         expect(request.contentType.parameters['charset'], equals(ASCII.name));
       });
 
+      test(
+          'setting encoding should not update content-type if content-type has been set manually',
+          () {
+        FormRequest request = new FormRequest();
+        expect(request.contentType.parameters['charset'], equals(UTF8.name));
+
+        // Manually override content-type.
+        request.contentType =
+            new MediaType('application', 'x-custom', {'charset': LATIN1.name});
+        expect(request.contentType.mimeType, equals('application/x-custom'));
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+
+        // Changes to encoding should no longer update the content-type.
+        request.encoding = ASCII;
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+      });
+
+      test('setting content-type should not be allowed once sent', () async {
+        Uri uri = Uri.parse('/test');
+        MockTransports.http.expect('GET', uri);
+        FormRequest request = new FormRequest();
+        await request.get(uri: uri);
+        expect(() {
+          request.contentType = new MediaType('application', 'x-custom');
+        }, throwsStateError);
+      });
+
       test('setting encoding should not be allowed once sent', () async {
         Uri uri = Uri.parse('/test');
         MockTransports.http.expect('GET', uri);
diff --git a/test/unit/http/json_request_test.dart b/test/unit/http/json_request_test.dart
index f9283269..cd4dbdf0 100644
--- a/test/unit/http/json_request_test.dart
+++ b/test/unit/http/json_request_test.dart
@@ -35,11 +35,6 @@ void main() {
         configureWTransportForTest();
       });
 
-      test('content-type cannot be set manually', () {
-        JsonRequest request = new JsonRequest();
-        expect(() => request.contentType = null, throwsUnsupportedError);
-      });
-
       test('setting entire body (Map)', () {
         Map json = {'field': 'value'};
         JsonRequest request = new JsonRequest()..body = json;
@@ -137,6 +132,33 @@ void main() {
         expect(request.contentType.parameters['charset'], equals(ASCII.name));
       });
 
+      test(
+          'setting encoding should not update content-type if content-type has been set manually',
+          () {
+        JsonRequest request = new JsonRequest();
+        expect(request.contentType.parameters['charset'], equals(UTF8.name));
+
+        // Manually override content-type.
+        request.contentType =
+            new MediaType('application', 'x-custom', {'charset': LATIN1.name});
+        expect(request.contentType.mimeType, equals('application/x-custom'));
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+
+        // Changes to encoding should no longer update the content-type.
+        request.encoding = ASCII;
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+      });
+
+      test('setting content-type should not be allowed once sent', () async {
+        Uri uri = Uri.parse('/test');
+        MockTransports.http.expect('GET', uri);
+        JsonRequest request = new JsonRequest();
+        await request.get(uri: uri);
+        expect(() {
+          request.contentType = new MediaType('application', 'x-custom');
+        }, throwsStateError);
+      });
+
       test('setting encoding should not be allowed once sent', () async {
         Uri uri = Uri.parse('/test');
         MockTransports.http.expect('GET', uri);
diff --git a/test/unit/http/plain_text_request_test.dart b/test/unit/http/plain_text_request_test.dart
index c4ebd8c4..9404da92 100644
--- a/test/unit/http/plain_text_request_test.dart
+++ b/test/unit/http/plain_text_request_test.dart
@@ -35,11 +35,6 @@ void main() {
         configureWTransportForTest();
       });
 
-      test('content-type cannot be set manually', () {
-        Request request = new Request();
-        expect(() => request.contentType = null, throwsUnsupportedError);
-      });
-
       test('setting body (string)', () {
         Request request = new Request();
 
@@ -133,6 +128,33 @@ void main() {
         expect(request.contentType.parameters['charset'], equals(ASCII.name));
       });
 
+      test(
+          'setting encoding should not update content-type if content-type has been set manually',
+          () {
+        Request request = new Request();
+        expect(request.contentType.parameters['charset'], equals(UTF8.name));
+
+        // Manually override content-type.
+        request.contentType =
+            new MediaType('application', 'x-custom', {'charset': LATIN1.name});
+        expect(request.contentType.mimeType, equals('application/x-custom'));
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+
+        // Changes to encoding should no longer update the content-type.
+        request.encoding = ASCII;
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+      });
+
+      test('setting content-type should not be allowed once sent', () async {
+        Uri uri = Uri.parse('/test');
+        MockTransports.http.expect('GET', uri);
+        Request request = new Request();
+        await request.get(uri: uri);
+        expect(() {
+          request.contentType = new MediaType('application', 'x-custom');
+        }, throwsStateError);
+      });
+
       test('setting encoding should not be allowed once sent', () async {
         Uri uri = Uri.parse('/test');
         MockTransports.http.expect('GET', uri);
diff --git a/test/unit/http/streamed_request_test.dart b/test/unit/http/streamed_request_test.dart
index 744cf857..6a451b6d 100644
--- a/test/unit/http/streamed_request_test.dart
+++ b/test/unit/http/streamed_request_test.dart
@@ -115,6 +115,33 @@ void main() {
         expect(request.contentType.parameters['charset'], equals(ASCII.name));
       });
 
+      test(
+          'setting encoding should not update content-type if content-type has been set manually',
+          () {
+        StreamedRequest request = new StreamedRequest();
+        expect(request.contentType.parameters['charset'], equals(UTF8.name));
+
+        // Manually override content-type.
+        request.contentType =
+            new MediaType('application', 'x-custom', {'charset': LATIN1.name});
+        expect(request.contentType.mimeType, equals('application/x-custom'));
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+
+        // Changes to encoding should no longer update the content-type.
+        request.encoding = ASCII;
+        expect(request.contentType.parameters['charset'], equals(LATIN1.name));
+      });
+
+      test('setting content-type should not be allowed once sent', () async {
+        Uri uri = Uri.parse('/test');
+        MockTransports.http.expect('GET', uri);
+        StreamedRequest request = new StreamedRequest();
+        await request.get(uri: uri);
+        expect(() {
+          request.contentType = new MediaType('application', 'x-custom');
+        }, throwsStateError);
+      });
+
       test('setting encoding should not be allowed once sent', () async {
         Uri uri = Uri.parse('/test');
         MockTransports.http.expect('GET', uri);