diff --git a/HISTORY.md b/HISTORY.md
index a2e8a75..e33a289 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,6 +1,17 @@
 Sanitize History
 ================================================================================
 
+Version 3.1.2 (git)
+-------------------
+
+* Fixed: Deleting a node in a custom transformer could trigger a memory leak
+  in Nokogiri if that node's children were later reparented, which the built-in
+  CleanElement transformer did by default. The CleanElement transformer is now
+  careful not to reparent the children of deleted nodes. [#129]
+
+[129]:https://github.com/rgrove/sanitize/issues/129
+
+
 Version 3.1.1 (2015-02-04)
 --------------------------
 
diff --git a/lib/sanitize/transformers/clean_element.rb b/lib/sanitize/transformers/clean_element.rb
index 0b1bdf3..7e2be30 100644
--- a/lib/sanitize/transformers/clean_element.rb
+++ b/lib/sanitize/transformers/clean_element.rb
@@ -55,8 +55,13 @@ def call(env)
 
     name = env[:node_name]
 
-    # Delete any element that isn't in the config whitelist.
-    unless @elements.include?(name)
+    # Delete any element that isn't in the config whitelist, unless the node has
+    # already been deleted from the document.
+    #
+    # It's important that we not try to reparent the children of a node that has
+    # already been deleted, since that seems to trigger a memory leak in
+    # Nokogiri.
+    unless @elements.include?(name) || node.parent.nil?
       # Elements like br, div, p, etc. need to be replaced with whitespace in
       # order to preserve readability.
       if @whitespace_elements.include?(name)