diff --git a/lib/rdf/util/cache.rb b/lib/rdf/util/cache.rb
index 7c2e25b3..56fd5598 100644
--- a/lib/rdf/util/cache.rb
+++ b/lib/rdf/util/cache.rb
@@ -85,7 +85,7 @@ def []=(key, value)
           id = value.__id__
           @cache[key] = id
           @index[id] = key
-          ObjectSpace.define_finalizer(value, proc {|id| @cache.delete(@index.delete(id))})
+          ObjectSpace.define_finalizer(value, finalizer_proc)
         end
         value
       end
@@ -100,6 +100,12 @@ def delete(key)
         @cache.delete(key)
         @index.delete(id) if id
       end
+
+      private
+
+      def finalizer_proc
+        proc { |id| @cache.delete(@index.delete(id)) }
+      end
     end # ObjectSpaceCache
 
     ##
diff --git a/spec/util/cache_spec.rb b/spec/util/cache_spec.rb
new file mode 100644
index 00000000..c22a521e
--- /dev/null
+++ b/spec/util/cache_spec.rb
@@ -0,0 +1,80 @@
+require_relative '../spec_helper'
+
+describe RDF::Util::Cache do
+  subject(:cache) do
+    described_class.new(10)
+  end
+
+  describe '#capacity' do
+    it 'returns the cache size' do
+      expect(cache.capacity).to eq 10
+    end
+  end
+
+  describe '#size' do
+    it 'returns the cache size' do
+      cache[:key] = {}
+      expect(cache.size).to eq 1
+    end
+  end
+
+  describe '#[]' do
+    it 'returns the value' do
+      cache[:key] = {}
+      expect(cache[:key]).to eq({})
+    end
+  end
+
+  describe '#[]=' do
+    context 'when the cache is not full' do
+      it 'stores the value' do
+        expect {
+          cache[:key] = {}
+        }.to change(cache, :size).by(1)
+      end
+
+      it 'returns the value' do
+        expect(cache[:key] = {}).to eq({})
+      end
+    end
+
+    context 'when the cache is full' do
+      before do
+        10.times { |i| cache[i] = {} }
+      end
+
+      it 'does not store the value' do
+        expect {
+          cache[:key] = {}
+        }.not_to change(cache, :size)
+      end
+
+      it 'returns the value' do
+        expect(cache[:key] = {}).to eq({})
+      end
+    end
+  end
+
+  context 'when the GC starts' do
+    before do
+      100.times { |i| cache[i] = {}; nil }
+    end
+
+    # Sometimes the last reference is not gc
+    it 'cleans the unused references' do
+      expect {
+        GC.start
+      }.to change(cache, :size).by_at_most(-9)
+    end
+  end
+
+  describe '#delete' do
+    before do
+      cache[:key] = {}
+    end
+
+    it 'delete the value' do
+      expect { cache.delete(:key) }.to change(cache, :size).to(0)
+    end
+  end
+end
\ No newline at end of file