diff --git a/plugins/python/python_plugin.c b/plugins/python/python_plugin.c
index 8dd57a35..c05686a5 100644
--- a/plugins/python/python_plugin.c
+++ b/plugins/python/python_plugin.c
@@ -127,6 +127,8 @@ struct uwsgi_option uwsgi_python_options[] = {
 	{"py-auto-reload-ignore", required_argument, 0, "ignore the specified module during auto-reload scan (can be specified multiple times)", uwsgi_opt_add_string_list, &up.auto_reload_ignore, UWSGI_OPT_THREADS|UWSGI_OPT_MASTER},
 #endif
 
+	{"start_response-nodelay", no_argument, 0, "send WSGI http headers as soon as possible (PEP violation)", uwsgi_opt_true, &up.start_response_nodelay, 0},
+
 	{0, 0, 0, 0, 0, 0, 0},
 };
 
diff --git a/plugins/python/uwsgi_python.h b/plugins/python/uwsgi_python.h
index 275a2798..4f189e88 100644
--- a/plugins/python/uwsgi_python.h
+++ b/plugins/python/uwsgi_python.h
@@ -178,6 +178,7 @@ struct uwsgi_python {
 	PyObject *after_req_hook_args;
 
 	char *pyrun;
+	int start_response_nodelay;
 
 };
 
@@ -266,6 +267,7 @@ char *uwsgi_pythonize(char *);
 void *uwsgi_python_autoreloader_thread(void *);
 
 int uwsgi_python_manage_exceptions(void);
+int uwsgi_python_do_send_headers(struct wsgi_request *);
 
 #ifdef UWSGI_PYPY
 #undef UWSGI_MINTERPRETERS
diff --git a/plugins/python/wsgi_handlers.c b/plugins/python/wsgi_handlers.c
index 2b91ef14..659fc430 100644
--- a/plugins/python/wsgi_handlers.c
+++ b/plugins/python/wsgi_handlers.c
@@ -267,16 +267,21 @@ PyTypeObject uwsgi_InputType = {
 PyObject *py_uwsgi_write(PyObject * self, PyObject * args) {
 	PyObject *data;
 	char *content;
-	int len;
+	size_t content_len;
 
 	struct wsgi_request *wsgi_req = current_wsgi_req();
 
 	data = PyTuple_GetItem(args, 0);
 	if (PyString_Check(data)) {
 		content = PyString_AsString(data);
-		len = PyString_Size(data);
+		content_len = PyString_Size(data);
+		if (content_len > 0 && !wsgi_req->headers_sent) {
+                        if (uwsgi_python_do_send_headers(wsgi_req)) {
+                                return NULL;
+                        }
+                }
 		UWSGI_RELEASE_GIL
-			wsgi_req->response_size = wsgi_req->socket->proto_write(wsgi_req, content, len);
+			wsgi_req->response_size = wsgi_req->socket->proto_write(wsgi_req, content, content_len);
 		UWSGI_GET_GIL
 		// this is a special case for the write callable
 		// no need to honout write-errors-exception-only
diff --git a/plugins/python/wsgi_headers.c b/plugins/python/wsgi_headers.c
index d7ed9285..57033f6b 100644
--- a/plugins/python/wsgi_headers.c
+++ b/plugins/python/wsgi_headers.c
@@ -19,6 +19,11 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 
 	int base = 0;
 
+	// avoid double sending of headers
+	if (wsgi_req->headers_sent) {
+		return PyErr_Format(PyExc_IOError, "headers already sent");
+	}
+
 	// this must be done before headers management
 	if (PyTuple_Size(args) > 2) {
 		exc_info = PyTuple_GetItem(args, 2);
@@ -45,7 +50,7 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 
 	head = PyTuple_GetItem(args, 0);
 	if (!head) {
-		goto clear;
+		return PyErr_Format(PyExc_TypeError, "start_response() takes at least 2 arguments");
 	}
 
 #ifdef PYTHREE
@@ -53,8 +58,7 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 #else
 	if (!PyString_Check(head)) {
 #endif
-		uwsgi_log( "http status must be a string !\n");
-		goto clear;
+		return PyErr_Format(PyExc_TypeError, "http status must be a string");
 	}
 
 
@@ -101,12 +105,13 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 	}
 
 	headers = PyTuple_GetItem(args, 1);
-	if (!headers) goto clear;
+	if (!headers) {
+		return PyErr_Format(PyExc_TypeError, "start_response() takes at least 2 arguments");
+	}
 
 
 	if (!PyList_Check(headers)) {
-		uwsgi_log( "http headers must be in a python list\n");
-		goto clear;
+		return PyErr_Format(PyExc_TypeError, "http headers must be in a python list");
 	}
 	wsgi_req->header_cnt = PyList_Size(headers);
 
@@ -117,20 +122,36 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 		j = (i * 4) + base;
 		head = PyList_GetItem(headers, i);
 		if (!head) {
+			PyErr_Print();
 			goto clear;
 		}
 		if (!PyTuple_Check(head)) {
-			uwsgi_log( "http header must be defined in a tuple !\n");
-			goto clear;
+			return PyErr_Format(PyExc_TypeError, "http header must be defined in a tuple");
 		}
 		h_key = PyTuple_GetItem(head, 0);
 		if (!h_key) {
-			goto clear;
+			return PyErr_Format(PyExc_TypeError, "http header must be a 2-item tuple");
+		}
+#ifdef PYTHREE
+       		if (!PyUnicode_Check(h_key)) {
+#else
+        	if (!PyString_Check(h_key)) {
+#endif
+			return PyErr_Format(PyExc_TypeError, "http header key must be a string");
 		}
 		h_value = PyTuple_GetItem(head, 1);
 		if (!h_value) {
-			goto clear;
+			return PyErr_Format(PyExc_TypeError, "http header must be a 2-item tuple");
 		}
+#ifdef PYTHREE
+       		if (!PyUnicode_Check(h_value)) {
+#else
+        	if (!PyString_Check(h_value)) {
+#endif
+			return PyErr_Format(PyExc_TypeError, "http header value must be a string");
+		}
+
+		
 
 #ifdef PYTHREE
 		wsgi_req->hvec[j].iov_base = PyBytes_AsString(PyUnicode_AsASCIIString(h_key));
@@ -181,30 +202,13 @@ PyObject *py_uwsgi_spit(PyObject * self, PyObject * args) {
 	wsgi_req->hvec[j].iov_base = nl;
 	wsgi_req->hvec[j].iov_len = NL_SIZE;
 
-#ifdef __sun__
-	int remains = j + 1;
-	int iov_size;
-	struct iovec* iov_ptr = wsgi_req->hvec;
-	ssize_t iov_ret;
-	while(remains) {
-		iov_size = UMIN(remains, IOV_MAX);
-		UWSGI_RELEASE_GIL
-		iov_ret = wsgi_req->socket->proto_writev_header(wsgi_req, iov_ptr, iov_size);
-		UWSGI_GET_GIL
-		wsgi_req->headers_size += iov_ret;
-		iov_ptr += iov_size;
-		remains -= iov_size;
-	}
-#else
-	UWSGI_RELEASE_GIL
-		wsgi_req->headers_size = wsgi_req->socket->proto_writev_header(wsgi_req, wsgi_req->hvec, j + 1);
-	UWSGI_GET_GIL
-#endif
+	wsgi_req->headers_hvec = j;
 
-	if (wsgi_req->write_errors > uwsgi.write_errors_tolerance) {
-        	uwsgi_py_write_set_exception(wsgi_req);
-                return NULL;
-        }
+	if (up.start_response_nodelay) {
+		if (uwsgi_python_do_send_headers(wsgi_req)) {
+			return NULL;
+		}
+	}
 
 	//uwsgi_log("%d %p\n", wsgi_req->poll.fd, up.wsgi_writeout);
 	Py_INCREF(up.wsgi_writeout);
@@ -216,3 +220,36 @@ clear:
 	Py_INCREF(Py_None);
 	return Py_None;
 }
+
+int uwsgi_python_do_send_headers(struct wsgi_request *wsgi_req) {
+
+#ifdef __sun__
+        int remains = wsgi_req->headers_hvec + 1;
+        int iov_size;
+        struct iovec* iov_ptr = wsgi_req->hvec;
+        ssize_t iov_ret;
+        while(remains) {
+                iov_size = UMIN(remains, IOV_MAX);
+                UWSGI_RELEASE_GIL
+                iov_ret = wsgi_req->socket->proto_writev_header(wsgi_req, iov_ptr, iov_size);
+                UWSGI_GET_GIL
+                wsgi_req->headers_size += iov_ret;
+                iov_ptr += iov_size;
+                remains -= iov_size;
+        }
+#else
+        UWSGI_RELEASE_GIL
+                wsgi_req->headers_size = wsgi_req->socket->proto_writev_header(wsgi_req, wsgi_req->hvec, wsgi_req->headers_hvec + 1);
+        UWSGI_GET_GIL
+#endif
+
+	wsgi_req->headers_sent = 1;
+
+        if (wsgi_req->write_errors > uwsgi.write_errors_tolerance) {
+                uwsgi_py_write_set_exception(wsgi_req);
+                return -1;
+        }
+
+	return 0;
+
+}
diff --git a/plugins/python/wsgi_subhandler.c b/plugins/python/wsgi_subhandler.c
index ce048b59..0fb0e782 100644
--- a/plugins/python/wsgi_subhandler.c
+++ b/plugins/python/wsgi_subhandler.c
@@ -166,6 +166,11 @@ int uwsgi_response_subhandler_wsgi(struct wsgi_request *wsgi_req) {
 	if (PyString_Check((PyObject *)wsgi_req->async_result)) {
 		char *content = PyString_AsString(wsgi_req->async_result);
 		size_t content_len = PyString_Size(wsgi_req->async_result);
+		if (content_len > 0 && !wsgi_req->headers_sent) {
+			if (uwsgi_python_do_send_headers(wsgi_req)) {
+				goto clear;
+			}
+		}
 		UWSGI_RELEASE_GIL
 		wsgi_req->response_size += wsgi_req->socket->proto_write(wsgi_req, content, content_len);
 		UWSGI_GET_GIL
@@ -252,6 +257,11 @@ int uwsgi_response_subhandler_wsgi(struct wsgi_request *wsgi_req) {
 	if (PyString_Check(pychunk)) {
 		char *content = PyString_AsString(pychunk);
 		size_t content_len = PyString_Size(pychunk);
+		if (content_len > 0 && !wsgi_req->headers_sent) {
+                        if (uwsgi_python_do_send_headers(wsgi_req)) {
+                                goto clear;
+                        }
+                }
 		UWSGI_RELEASE_GIL
 		wsgi_req->response_size += wsgi_req->socket->proto_write(wsgi_req, content, content_len);
 		UWSGI_GET_GIL
diff --git a/uwsgi.h b/uwsgi.h
index fe316260..460aa40a 100644
--- a/uwsgi.h
+++ b/uwsgi.h
@@ -935,6 +935,10 @@ struct wsgi_request {
 	// current socket mapped to request
 	struct uwsgi_socket *socket;
 
+	// check if headers are already sent
+	int headers_sent;
+	int headers_hvec;
+
 	int body_as_file;
 	//for generic use
 	size_t buf_pos;