diff --git a/AUTHORS b/AUTHORS
index d71461d9..686d4447 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -7,3 +7,4 @@ Ib Lundgren
 Daniel Greenfeld
 Caleb Brown
 Donald Stufft
+Michael Vogt
\ No newline at end of file
diff --git a/oauthlib/oauth1/rfc5849/__init__.py b/oauthlib/oauth1/rfc5849/__init__.py
index accfe1c6..d370525e 100644
--- a/oauthlib/oauth1/rfc5849/__init__.py
+++ b/oauthlib/oauth1/rfc5849/__init__.py
@@ -110,7 +110,7 @@ def get_oauth_params(self):
 
         return params
 
-    def _render(self, request, formencode=False):
+    def _render(self, request, formencode=False, realm=None):
         """Render a signed request according to signature type
 
         Returns a 3-tuple containing the request URI, headers, and body.
@@ -131,7 +131,7 @@ def _render(self, request, formencode=False):
         # like the spec requires. This would be a fundamental change though, and
         # I'm not sure how I feel about it.
         if self.signature_type == SIGNATURE_TYPE_AUTH_HEADER:
-            headers = parameters.prepare_headers(request.oauth_params, request.headers, self.realm)
+            headers = parameters.prepare_headers(request.oauth_params, request.headers, realm=realm)
         elif self.signature_type == SIGNATURE_TYPE_BODY and request.decoded_body is not None:
             body = parameters.prepare_form_encoded_body(request.oauth_params, request.decoded_body)
             if formencode:
@@ -144,7 +144,7 @@ def _render(self, request, formencode=False):
 
         return uri, headers, body
 
-    def sign(self, uri, http_method=u'GET', body=None, headers=None):
+    def sign(self, uri, http_method=u'GET', body=None, headers=None, realm=None):
         """Sign a request
 
         Signs an HTTP request with the specified parts.
@@ -212,7 +212,8 @@ def sign(self, uri, http_method=u'GET', body=None, headers=None):
         request.oauth_params.append((u'oauth_signature', self.get_oauth_signature(request)))
 
         # render the signed request and return it
-        return self._render(request, formencode=True)
+        return self._render(request, formencode=True,
+                            realm=(realm or self.realm))
 
 
 class Server(object):