diff --git a/libmproxy/protocol/http.py b/libmproxy/protocol/http.py
index 05657ea66..93065b47e 100644
--- a/libmproxy/protocol/http.py
+++ b/libmproxy/protocol/http.py
@@ -631,8 +631,10 @@ class HTTPRequest(HTTPMessage):
             host = self.headers.get_first("host")
         if not host:
             host = self.host
-        host = host.encode("idna")
-        return host
+        if host:
+            return host.encode("idna")
+        else:
+            return None
 
     def pretty_url(self, hostheader):
         if self.form_out == "authority":  # upstream proxy mode