diff --git a/warcprox/mitmproxy.py b/warcprox/mitmproxy.py
index e2cc321..f6ea742 100644
--- a/warcprox/mitmproxy.py
+++ b/warcprox/mitmproxy.py
@@ -172,8 +172,8 @@ class ProxyingRecordingHTTPResponse(http_client.HTTPResponse):
         self.msg['Via'] = via_header_value(
                 self.msg.get('Via'), '%0.1f' % (self.version / 10.0))
         if extra_response_headers:
-            rmeta = {"capture-metadata": extra_response_headers}
-            self.msg['Warcprox-Meta'] = json.dumps(rmeta, separators=',:')
+            for header, value in extra_response_headers.items():
+                self.msg[header] = value
 
         for k,v in self.msg.items():
             if k.lower() not in (
diff --git a/warcprox/warcproxy.py b/warcprox/warcproxy.py
index ec613ab..d37e588 100644
--- a/warcprox/warcproxy.py
+++ b/warcprox/warcproxy.py
@@ -182,7 +182,8 @@ class WarcProxyHandler(warcprox.mitmproxy.MitmProxyHandler):
         extra_response_headers = {}
         if warcprox_meta and 'accept' in warcprox_meta and \
                 'capture-metadata' in warcprox_meta['accept']:
-            extra_response_headers['timestamp'] = timestamp.strftime('%Y-%m-%dT%H:%M:%SZ')
+            rmeta = {'capture-metadata': {'timestamp': timestamp.strftime('%Y-%m-%dT%H:%M:%SZ')}}
+            extra_response_headers['Warcprox-Meta'] = json.dumps(rmeta, separators=',:')
 
         req, prox_rec_res = warcprox.mitmproxy.MitmProxyHandler._proxy_request(
                 self, extra_response_headers=extra_response_headers)