diff --git a/src/calibre/ebooks/oeb/transforms/split.py b/src/calibre/ebooks/oeb/transforms/split.py
index 1a707484b3..004cb1ebe1 100644
--- a/src/calibre/ebooks/oeb/transforms/split.py
+++ b/src/calibre/ebooks/oeb/transforms/split.py
@@ -254,7 +254,7 @@ class FlowSplitter(object):
                     self.trees[i:i+1] = [before_tree, after_tree]
                     break
 
-        trees, ids = [], set([])
+        trees, ids = [], set()
         for tree in self.trees:
             root = tree.getroot()
             if self.is_page_empty(root):
@@ -267,10 +267,10 @@ class FlowSplitter(object):
                 if ids:
                     body = self.get_body(root)
                     if body is not None:
-                        for x in ids:
-                            body.insert(0, body.makeelement(XHTML('div'),
-                                id=x, style='height:0pt'))
-                ids = set([])
+                        existing_ids = frozenset(body.xpath('//*/@id'))
+                        for x in ids - existing_ids:
+                            body.insert(0, body.makeelement(XHTML('div'), id=x, style='height:0pt'))
+                ids = set()
                 trees.append(tree)
         self.trees = trees