diff --git a/mitmproxy/proxy/protocol/http.py b/mitmproxy/proxy/protocol/http.py
index 66390e152..2ae656b3e 100644
--- a/mitmproxy/proxy/protocol/http.py
+++ b/mitmproxy/proxy/protocol/http.py
@@ -291,7 +291,7 @@ class HttpLayer(base.Layer):
             self.channel.ask("error", f)
             raise exceptions.ProtocolException(
                 "HTTP protocol error in client request: {}".format(e)
-            )
+            ) from e
 
         self.log("request", "debug", [repr(request)])