diff --git a/app/controllers/reducers_controller.rb b/app/controllers/reducers_controller.rb
index 3afaabdd6..330194d9d 100644
--- a/app/controllers/reducers_controller.rb
+++ b/app/controllers/reducers_controller.rb
@@ -43,9 +43,14 @@ def create
 
     filters = new_params.fetch('filters', {})
     if filters.has_key?('extractor_keys') && filters['extractor_keys'].is_a?(String)
-      filters['extractor_keys'] = JSON.parse(filters['extractor_keys'])
+      begin
+        filters['extractor_keys'] = JSON.parse(filters['extractor_keys'])
+      rescue JSON::ParserError, TypeError;
+      end
     end
 
+    reset_config_reducer_keys(new_params)
+
     @reducer = reducer_class.new(new_params)
 
     respond_to do |format|
@@ -69,9 +74,14 @@ def update
 
     filters = params.fetch('filters', {})
     if filters.has_key?('extractor_keys') && filters['extractor_keys'].is_a?(String)
-      filters['extractor_keys'] = JSON.parse(filters['extractor_keys'])
+      begin
+        filters['extractor_keys'] = JSON.parse(filters['extractor_keys'])
+      rescue JSON::ParserError, TypeError;
+      end
     end
 
+    reset_config_reducer_keys(params)
+
     @reducer.update(params)
 
     respond_to do |format|
@@ -122,6 +132,8 @@ def reducer_params(klass)
     params.require(:reducer).permit(
       :key,
       :topic,
+      :user_reducer_keys,
+      :subject_reducer_keys,
       *klass.configuration_fields.keys,
       filters: {},
       grouping: {},
@@ -131,4 +143,15 @@ def reducer_params(klass)
   def record_not_valid(exception)
     render json: { error: exception.message }, status: 422
   end
+
+  def reset_config_reducer_keys(param_object)
+    if param_object[:topic] == 'reduce_by_subject'
+      param_object[:subject_reducer_keys] = nil
+    elsif param_object[:topic] == 'reduce_by_user'
+      param_object[:user_reducer_keys] = nil
+    else
+      param_object[:subject_reducer_keys] = nil
+      param_object[:user_reducer_keys] = nil
+    end
+  end
 end
diff --git a/app/views/reducers/_form.html.erb b/app/views/reducers/_form.html.erb
index 6045e10c5..16b3c5bbd 100644
--- a/app/views/reducers/_form.html.erb
+++ b/app/views/reducers/_form.html.erb
@@ -15,6 +15,15 @@
 
   <%= f.input :reducible_type, :as => :hidden %>
 
+  <div id='user_reducer_keys'>
+    <%= f.input :user_reducer_keys%>
+  </div>
+
+
+  <div id='subject_reducer_keys'>
+    <%= f.input :subject_reducer_keys%>
+  </div>
+
   <div class="panel panel-info">
     <div class="panel-heading"><a role="button" data-toggle="collapse" href="#groupingInputs" aria-expanded="false" aria-controls="groupingInputs">Grouping <span class="caret"></span></a></div>
     <div class="panel-body collapse" id="groupingInputs">
@@ -50,3 +59,25 @@
     <%= link_to 'Back', project_path(@reducible, anchor: 'reducers'), class: 'btn btn-default' %>
   <% end %>
 <% end %>
+
+<script type="text/javascript">
+  function toggle_reducer_keys_inputs(topic) {
+    if (topic.includes('subject')){
+      $('#subject_reducer_keys').hide()
+      $('#user_reducer_keys').show()
+    } else {
+      $('#subject_reducer_keys').show()
+      $('#user_reducer_keys').hide()
+    }
+  }
+
+  $(function() {
+    var reducer_topic = $('#reducer_topic').val();
+    toggle_reducer_keys_inputs(reducer_topic)
+  });
+
+  $('#reducer_topic').on('change', function(event){
+    var reducer_topic = event.target.value;
+    toggle_reducer_keys_inputs(reducer_topic)
+  })
+</script>
\ No newline at end of file
diff --git a/spec/controllers/reducers_controller_spec.rb b/spec/controllers/reducers_controller_spec.rb
index b9547228b..1b9671ab0 100644
--- a/spec/controllers/reducers_controller_spec.rb
+++ b/spec/controllers/reducers_controller_spec.rb
@@ -96,6 +96,16 @@
         expect(workflow.reducers.first.filters['extractor_keys']).to eq(['test'])
       end
 
+      it 'saves extractor_keys in inputted format' do
+        nested_reducer_params[:filters][:extractor_keys] = '[\'test\']'
+        post :create, params: {
+          workflow_id: workflow.id,
+          reducer: nested_reducer_params
+        }, format: :json
+
+        expect(workflow.reducers.first.filters['extractor_keys']).to eq('[\'test\']')
+      end
+
       it 'jsonifies extractor_keys' do
         post :create, params: {
           workflow_id: workflow.id,
@@ -147,6 +157,44 @@
                               reducer: {key: nil, type: 'external'}}
         expect(response.status).to eq(200)
       end
+
+      context 'when topic is reduce_by_subject' do
+        it 'sets subject_reducer_keys to nil' do
+          put :update, params: {
+            workflow_id: workflow.id,
+            id: reducer.id,
+            reducer: {
+              url: 'https://example.org/2',
+              user_reducer_keys: 'user_reducer_keys_value',
+              subject_reducer_keys: 'subject_reducer_keys',
+              topic: 'reduce_by_subject'
+            }
+          }
+
+          reducer.reload
+          expect(reducer.subject_reducer_keys).to be_nil
+          expect(reducer.user_reducer_keys).to eq('user_reducer_keys_value')
+        end
+      end
+
+      context 'when topic is not reduce_by_subject' do
+        it 'sets user_reducer_keys to nil' do
+          put :update, params: {
+            workflow_id: workflow.id,
+            id: reducer.id,
+            reducer: {
+              url: 'https://example.org/2',
+              user_reducer_keys: 'user_reducer_keys_value',
+              subject_reducer_keys: 'subject_reducer_keys_value',
+              topic: 'reduce_by_user'
+            }
+          }
+
+          reducer.reload
+          expect(reducer.subject_reducer_keys).to eq('subject_reducer_keys_value')
+          expect(reducer.user_reducer_keys).to be_nil
+        end
+      end
     end
   end
 end