diff --git a/libmproxy/dump.py b/libmproxy/dump.py
index c464644c4..59e46dbbb 100644
--- a/libmproxy/dump.py
+++ b/libmproxy/dump.py
@@ -171,7 +171,7 @@ class DumpMaster(flow.FlowMaster):
 
     def _print_message(self, message):
         if self.o.flow_detail >= 2:
-            print(self.indent(4, message.headers), file=self.outfile)
+            print(self.indent(4, message.headers.format()), file=self.outfile)
         if self.o.flow_detail >= 3:
             if message.content == http.CONTENT_MISSING:
                 print(self.indent(4, "(content missing)"), file=self.outfile)
diff --git a/libmproxy/flow.py b/libmproxy/flow.py
index a010bb399..553bfd844 100644
--- a/libmproxy/flow.py
+++ b/libmproxy/flow.py
@@ -268,7 +268,7 @@ class ServerPlaybackState:
                 # to prevent a mismatch between unicode/non-unicode.
                 v = [str(x) for x in v]
                 hdrs.append((i, v))
-            key.append(repr(hdrs))
+            key.append(hdrs)
         return hashlib.sha256(repr(key)).digest()
 
     def next_flow(self, request):
diff --git a/libmproxy/protocol/http.py b/libmproxy/protocol/http.py
index eb7749ea6..da6b8aa67 100644
--- a/libmproxy/protocol/http.py
+++ b/libmproxy/protocol/http.py
@@ -469,7 +469,7 @@ class HTTPRequest(HTTPMessage):
         if self.content or self.content == "":
             headers["Content-Length"] = [str(len(self.content))]
 
-        return str(headers)
+        return headers.format()
 
     def _assemble_head(self, form=None):
         return "%s\r\n%s\r\n" % (
@@ -823,7 +823,7 @@ class HTTPResponse(HTTPMessage):
         if self.content or self.content == "":
             headers["Content-Length"] = [str(len(self.content))]
 
-        return str(headers)
+        return headers.format()
 
     def _assemble_head(self, preserve_transfer_encoding=False):
         return '%s\r\n%s\r\n' % (