Index: http/__init__.py
===================================================================
--- http/__init__.py	(revision 9679)
+++ http/__init__.py	(working copy)
@@ -263,6 +263,9 @@
         cookiedict[key] = c.get(key).value
     return cookiedict
 
+class BadHeaderError(ValueError):
+    pass
+
 class HttpResponse(object):
     """A basic HTTP response, with content and dictionary-accessed headers."""
 
@@ -301,6 +304,8 @@
     def _convert_to_ascii(self, *values):
         """Converts all values to ascii strings."""
         for value in values:
+            if '\n' in value or '\r' in value:
+                raise BadHeaderError("Header values can't contain newlines (got %r)" % (value))
             if isinstance(value, unicode):
                 try:
                     yield value.encode('us-ascii')