diff --git a/scour/scour.py b/scour/scour.py
index ad675e6..95e24b5 100644
--- a/scour/scour.py
+++ b/scour/scour.py
@@ -715,22 +715,36 @@ def shortenIDs(doc, prefix, options):
     idList.extend([rid for rid in identifiedElements if rid not in idList])
     # Ensure we do not reuse a protected ID by accident
     protectedIDs = protected_ids(identifiedElements, options)
+    # IDs that we have used "ahead of time".  Happens if we are about to
+    # rename an ID and there is no length difference between the new and
+    # the old ID.
+    consumedIDs = set()
 
     curIdNum = 1
 
     for rid in idList:
         curId = intToID(curIdNum, prefix)
 
-        # Skip ahead if the new ID is in use and protected.
-        while curId in protectedIDs:
+        # Skip ahead if the new ID has already been used or is protected.
+        while curId in protectedIDs or curId in consumedIDs:
             curIdNum += 1
             curId = intToID(curIdNum, prefix)
 
-        # Now check if we found a new ID (we can happen to choose the same
-        # ID.  More likely on a rerun)
-        if curId != rid:
+        # Avoid checking the ID if it will not affect the size of the document
+        # (e.g. remapping "c" to "a" is not going to win us anything)
+        if len(curId) != len(rid):
             # Then go rename it.
             num += renameID(doc, rid, curId, identifiedElements, referencedIDs)
+        elif curId < rid:
+            # If we skip reassigning an ID because it has the same length
+            # (E.g. skipping "c" -> "a"), then we have to mark the "future"
+            # ID as taken ("c" in the example).
+            # The "strictly less than" in the condition is to ensure that we
+            # properly update curIdNum in the corner case where curId == rid.
+            consumedIDs.add(rid)
+            # Use continue here without updating curIdNum to avoid losing
+            # the current ID.
+            continue
         curIdNum += 1
 
     return num
diff --git a/testscour.py b/testscour.py
index b52d98f..eb62af7 100755
--- a/testscour.py
+++ b/testscour.py
@@ -1948,6 +1948,19 @@ class ShortenIDsOption(unittest.TestCase):
                          'Did not update reference to shortened ID')
 
 
+class ShortenIDsStableOutput(unittest.TestCase):
+
+    def runTest(self):
+        doc = scourXmlFile('unittests/shorten-ids-stable-output.svg',
+                           parse_args(['--shorten-ids']))
+        use_tags = doc.getElementsByTagName('use')
+        hrefs_ordered = [x.getAttributeNS('http://www.w3.org/1999/xlink', 'href')
+                         for x in use_tags]
+        expected = ['#a', '#b', '#b']
+        self.assertEquals(hrefs_ordered, expected,
+                          '--shorten-ids pointlessly reassigned ids')
+
+
 class MustKeepGInSwitch(unittest.TestCase):
 
     def runTest(self):
diff --git a/unittests/shorten-ids-stable-output.svg b/unittests/shorten-ids-stable-output.svg
new file mode 100644
index 0000000..f2df1bc
--- /dev/null
+++ b/unittests/shorten-ids-stable-output.svg
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+ <defs>
+  <rect id="a" width="80" height="50" fill="red"/>
+  <rect id="b" width="80" height="50" fill="blue"/>
+ </defs>
+ <use xlink:href="#a"/>
+ <use xlink:href="#b"/>
+ <use xlink:href="#b"/>
+</svg>
+