diff -r 66d0f6ef2a7f Lib/test/test_urllib2net.py
--- a/Lib/test/test_urllib2net.py	Thu Feb 28 18:03:16 2013 +0200
+++ b/Lib/test/test_urllib2net.py	Sat Mar 02 22:05:02 2013 -0500
@@ -177,6 +177,22 @@
             opener.open(request)
             self.assertEqual(request.get_header('User-agent'),'Test-Agent')
 
+    def test_headers_with_spaces(self):
+        url = "http://www.example.com"
+        with support.transient_internet(url):
+            opener = urllib.request.build_opener()
+            request = urllib.request.Request(url)
+            # testing trailing space to be removed
+            request.add_header('Footrail ', 'bartrail')
+            self.assertTrue(request.headers['Footrail'], 'bartrail')
+            request.add_unredirected_header('Footrailu ', 'bartrailu')
+            self.assertTrue(request.unredirected_hdrs['Footrailu'], 'bartrailu')
+            # testing leading space to be removed
+            request.add_header(' Foolead', 'barlead')
+            self.assertTrue(request.headers['Foolead'], 'barlead')
+            request.add_unredirected_header(' Fooleadu', 'barleadu')
+            self.assertTrue(request.unredirected_hdrs['Fooleadu'], 'barleadu')
+
     def test_sites_no_connection_close(self):
         # Some sites do not send Connection: close header.
         # Verify that those work properly. (#issue12576)
diff -r 66d0f6ef2a7f Lib/urllib/request.py
--- a/Lib/urllib/request.py	Thu Feb 28 18:03:16 2013 +0200
+++ b/Lib/urllib/request.py	Sat Mar 02 22:05:02 2013 -0500
@@ -358,11 +358,11 @@
 
     def add_header(self, key, val):
         # useful for something like authentication
-        self.headers[key.capitalize()] = val
+        self.headers[key.strip().capitalize()] = val
 
     def add_unredirected_header(self, key, val):
         # will not be added to a redirected request
-        self.unredirected_hdrs[key.capitalize()] = val
+        self.unredirected_hdrs[key.strip().capitalize()] = val
 
     def has_header(self, header_name):
         return (header_name in self.headers or