diff --git a/klarnacheckout/connector.py b/klarnacheckout/connector.py
index e7067e3..af615ae 100644
--- a/klarnacheckout/connector.py
+++ b/klarnacheckout/connector.py
@@ -82,7 +82,11 @@ def apply(self, method, resource, options=None):
         if method == 'POST':
             req.add_header('Content-Type', content_type)
             data = options.get('data') or resource.marshal()
-            req.data = json.dumps(data).encode('utf-8')
+            if isinstance(data, (list, tuple, dict)):
+                # data which is iterable must be serialized
+                req.data = json.dumps(data).encode('utf-8')
+            else:
+                req.data = data.encode('utf-8')
 
         return self.handle_response(resource, self.opener.open(req))
 
diff --git a/tests/unit/test_order.py b/tests/unit/test_order.py
index 1a83104..7fb4690 100644
--- a/tests/unit/test_order.py
+++ b/tests/unit/test_order.py
@@ -97,6 +97,15 @@ def test_create(self):
         self._connector.apply.assert_called_once_with(
             "POST", self._order, {"url": location, "data": data})
 
+    def test_create_json(self):
+        location = "http://stub"
+        self._order.base_uri = location
+        data = '{"foo": "boo"}'
+        self._order.create(data)
+
+        self._connector.apply.assert_called_once_with(
+            "POST", self._order, {"url": location, "data": data})
+
     def test_fetch(self):
         location = "http://stub"
         self._order.location = location