Index: /trunk/reviewboard/contrib/tools/post-review
===================================================================
--- /trunk/reviewboard/contrib/tools/post-review	(revision 1849)
+++ /trunk/reviewboard/contrib/tools/post-review	(working copy)
@@ -1101,12 +1101,27 @@
         """
         Performs a diff between 2 revisions of a Subversion repository.
         """
+        def decrement_revision(revision):
+            """
+            Takes a revision string like r500 and decrements it to r499
+            """
+            def decrement_integers(match):
+                return str(int(match.group()) - 1)
+
+            my_re = re.compile(r'\d+')
+
+            return my_re.sub(decrement_integers, revision)
+
         if options.repository_url:
             revisions = revision_range.split(':')
             if len(revisions) < 1:
                 return None
             elif len(revisions) == 1:
-                revisions.append('HEAD')
+                # if we are given only one revision number, the submitter
+                # expects only the changes for that particular revision
+                # to be posted.  Thus: r500 becomes r499:r500
+                revisions.append(revisions[0])
+                revisions[0] = decrement_revision(revisions[0]);
 
             # if a new path was supplied at the command line, set it
             if len(args):