diff --git a/ahserver/globalEnv.py b/ahserver/globalEnv.py
index 3dced51..38e681f 100644
--- a/ahserver/globalEnv.py
+++ b/ahserver/globalEnv.py
@@ -50,7 +50,8 @@ def basic_auth_headers(user, passwd):
 
 async def stream_response(request, async_data_generator, content_type='text/html'):
 	res = StreamResponse()
-	res.content_type = content_type
+	if content_type:
+		res.content_type = content_type
 	res.set_status(200)
 	await res.prepare(request)
 	async for d in async_data_generator():