diff --git a/lib/oai/provider/response/list_identifiers.rb b/lib/oai/provider/response/list_identifiers.rb
index a58419d..4703ffb 100755
--- a/lib/oai/provider/response/list_identifiers.rb
+++ b/lib/oai/provider/response/list_identifiers.rb
@@ -1,7 +1,8 @@
 module OAI::Provider::Response
   
   class ListIdentifiers < RecordResponse
-    
+    required_parameters :metadata_prefix
+
     def to_xml
       result = provider.model.find(:all, options)
 
diff --git a/test/activerecord_provider/tc_ar_provider.rb b/test/activerecord_provider/tc_ar_provider.rb
index 30e1973..24fe109 100755
--- a/test/activerecord_provider/tc_ar_provider.rb
+++ b/test/activerecord_provider/tc_ar_provider.rb
@@ -53,8 +53,10 @@ def test_get_record_alternate_identifier_column
   end
 
   def test_list_identifiers
-    assert_nothing_raised { REXML::Document.new(@provider.list_identifiers) }
-    doc = REXML::Document.new(@provider.list_identifiers)
+    assert_nothing_raised do
+      REXML::Document.new(@provider.list_identifiers(:metadata_prefix => 'oai_dc'))
+    end
+    doc = REXML::Document.new(@provider.list_identifiers(:metadata_prefix => 'oai_dc'))
     assert_equal 100, doc.elements['OAI-PMH/ListIdentifiers'].to_a.size
   end
 
@@ -163,7 +165,7 @@ def test_handles_empty_collections
     test_metadata_formats
     # ListIdentifiers and ListRecords should return "noRecordsMatch" error code
     assert_raises(OAI::NoMatchException) do
-      REXML::Document.new(@provider.list_identifiers)
+      REXML::Document.new(@provider.list_identifiers(:metadata_prefix => 'oai_dc'))
     end
     assert_raises(OAI::NoMatchException) do
       REXML::Document.new(@provider.list_records(:metadata_prefix => 'oai_dc'))
diff --git a/test/provider/tc_provider.rb b/test/provider/tc_provider.rb
index 2e3d100..cf571c4 100644
--- a/test/provider/tc_provider.rb
+++ b/test/provider/tc_provider.rb
@@ -15,7 +15,8 @@ def test_additional_description
   end
 
   def test_list_identifiers_for_correct_xml
-    doc = REXML::Document.new(@mapped_provider.list_identifiers)
+    doc = REXML::Document.new(
+      @mapped_provider.list_identifiers(:metadata_prefix => 'oai_dc'))
     assert_not_nil doc.elements['OAI-PMH/request']
     assert_not_nil doc.elements['OAI-PMH/request/@verb']
     assert_not_nil doc.elements['OAI-PMH/ListIdentifiers']