diff --git a/lib/sbdb/environment.rb b/lib/sbdb/environment.rb
index 0e2011b..71f5ef9 100644
--- a/lib/sbdb/environment.rb
+++ b/lib/sbdb/environment.rb
@@ -1,5 +1,4 @@
 require 'bdb'
-require 'sbdb/weakhash'
 require 'sbdb/db'
 require 'sbdb/transaction'
 
diff --git a/lib/sbdb/weakhash.rb b/lib/sbdb/weakhash.rb
deleted file mode 100644
index eb57ff0..0000000
--- a/lib/sbdb/weakhash.rb
+++ /dev/null
@@ -1,59 +0,0 @@
-module SBDB
-  # See http://eigenclass.org/hiki/deferred-finalizers-in-Ruby
-  # Not threadsafe.
-  class WeakHash
-  	attr_reader :cache
-  	def initialize cache = ::Hash.new
-  		@cache = cache
-  		@key_map = {}
-  		@rev_cache = ::Hash.new { |h,k| h[k] = {} }
-  		@reclaim_value = lambda do |value_id| 
-  			if @rev_cache.has_key? value_id
-  				@rev_cache[value_id].each_key{ |key| @cache.delete key }
-  				@rev_cache.delete value_id
-  			end
-  		end
-  		@reclaim_key = lambda do |key_id|
-  			@cache.delete @key_map.delete(key_id) if @key_map.has_key? key_id
-  		end
-  	end
-
-  	def []=(key, value)
-  		case key
-  		when Fixnum, Symbol, true, false
-  			key2 = key
-  		else
-  			key2 = key.dup
-  		end
-  		@rev_cache[value.object_id][key2] = true
-  		@cache[key2] = value.object_id
-  		@key_map[key.object_id] = key2
-
-  		ObjectSpace.define_finalizer(value, @reclaim_value)
-  		ObjectSpace.define_finalizer(key, @reclaim_key)
-  		value
-  	end
-
-  	def [](key)
-  		value_id = @cache[key]
-  		return ObjectSpace._id2ref(value_id)  unless value_id.nil?
-  		nil
-  	rescue RangeError
-  		nil
-  	end
-
-  	def each(&e)
-  		@cache.each do |k, vid|
-  			unless vid.nil?
-  				obj =
-  				  begin
-  						ObjectSpace._id2ref vid
-  					rescue RangeError
-  						next
-  					end
-  				yield k, obj
-  			end
-  		end
-  	end
-  end
-end