diff --git a/lib/rack/cache/meta_store.rb b/lib/rack/cache/meta_store.rb
index 7fc63a9..ec37f35 100644
--- a/lib/rack/cache/meta_store.rb
+++ b/lib/rack/cache/meta_store.rb
@@ -38,7 +38,8 @@ def lookup(request, entity_store)
       return nil if match.nil?
 
       _, res = match
-      if body = entity_store.open(res['x-content-digest'])
+      entity_key = res['x-content-digest']
+      if entity_key && body = entity_store.open(entity_key)
         restore_response(res, body)
       else
         # the metastore referenced an entity that doesn't exist in
diff --git a/test/meta_store_test.rb b/test/meta_store_test.rb
index 69284c8..5071a81 100644
--- a/test/meta_store_test.rb
+++ b/test/meta_store_test.rb
@@ -190,6 +190,19 @@ def self.call(request); request.path_info.reverse end
         mock.verify
       end
 
+      it 'purges meta store entry when the entry does not contain the digest header' do
+        cache_key = store_simple_entry
+        meta_entry = @store.read(cache_key)
+        meta_entry.grep(Array).flatten.each { |h| h.is_a?(Hash) && h.delete('x-content-digest') }
+        @store.write(cache_key, meta_entry)
+        mock = Minitest::Mock.new
+        mock.expect :call, nil, [@store.cache_key(@request)]
+        @store.stub(:purge, mock) do
+          @store.lookup(@request, nil)
+        end
+        mock.verify
+      end
+
       it 'warns once if purge is not implemented' do
         store_simple_entry
         assert @response.headers['x-content-digest']