diff --git a/paramiko/dsskey.py b/paramiko/dsskey.py
index 5d46fc5..1901596 100644
--- a/paramiko/dsskey.py
+++ b/paramiko/dsskey.py
@@ -113,9 +113,9 @@ class DSSKey (PKey):
         rstr = util.deflate_long(r, 0)
         sstr = util.deflate_long(s, 0)
         if len(rstr) < 20:
-            rstr += zero_byte * (20 - len(rstr))
+            rstr = zero_byte * (20 - len(rstr)) + rstr
         if len(sstr) < 20:
-            sstr += zero_byte * (20 - len(sstr))
+            sstr = zero_byte * (20 - len(sstr)) + sstr
         m.add_string(rstr + sstr)
         return m
 
diff --git a/sites/www/changelog.rst b/sites/www/changelog.rst
index 2c4c1cf..cedc44f 100644
--- a/sites/www/changelog.rst
+++ b/sites/www/changelog.rst
@@ -2,6 +2,8 @@
 Changelog
 =========
 
+* :bug:`308` Fix regression in dsskey.py that caused sporadic signature 
+  verification failures. Thanks to Chris Rose.
 * :support:`299` Use deterministic signatures for ECDSA keys for improved
   security. Thanks to Alex Gaynor.
 * :support:`297` Replace PyCrypto's ``Random`` with `os.urandom` for improved