diff --git a/dio/lib/src/adapters/io_adapter.dart b/dio/lib/src/adapters/io_adapter.dart
index 430391075..23523a916 100644
--- a/dio/lib/src/adapters/io_adapter.dart
+++ b/dio/lib/src/adapters/io_adapter.dart
@@ -54,7 +54,7 @@ class DefaultHttpClientAdapter implements HttpClientAdapter {
 
       //Set Headers
       options.headers.forEach((k, v) {
-        if (v != null) request.headers.set(k, '$v');
+        if (v != null) request.headers.set(k, v);
       });
     } on SocketException catch (e) {
       if (e.message.contains('timed out')) {
diff --git a/dio/test/request_test.dart b/dio/test/request_test.dart
index d90881d17..5423edc92 100644
--- a/dio/test/request_test.dart
+++ b/dio/test/request_test.dart
@@ -86,6 +86,16 @@ void main() {
       assert(ri.method == 'GET');
     });
 
+
+    test('#test multi value headers', () async {
+      Response response = await dio.get(
+        '/multi-value-header',
+         options: Options(headers: {'x-multi-value-request-header': ['value1', 'value2']})
+      );
+      expect(response.statusCode, 200);
+      expect(response.headers.value("x-multi-value-request-header-echo"), equals('value1, value2'));
+    });
+
     test('#test request with URI', () async {
       Response response;
 
diff --git a/dio/test/utils.dart b/dio/test/utils.dart
index 3d6f6cc32..1ea2313e5 100644
--- a/dio/test/utils.dart
+++ b/dio/test/utils.dart
@@ -74,6 +74,17 @@ Future<void> startServer() async {
         return;
       }
 
+      if (path == '/multi-value-header') {
+        response.headers.contentType = ContentType('application', 'json');
+        response.headers.add("x-multi-value-request-header-echo", request.headers.value("x-multi-value-request-header").toString());
+        response
+          ..statusCode = 200
+          ..contentLength = -1
+          ..write('');
+        response.close();
+        return;
+      }
+
       if (path == '/download') {
         const content = 'I am a text file';
         response.headers.set('content-encoding', 'plain');