diff --git a/app/models/cost_query/custom_field_mixin.rb b/app/models/cost_query/custom_field_mixin.rb
index db14ca6686..30864ba85d 100644
--- a/app/models/cost_query/custom_field_mixin.rb
+++ b/app/models/cost_query/custom_field_mixin.rb
@@ -20,6 +20,10 @@ module CostQuery::CustomFieldMixin
     @all ||= generate_subclasses
   end
 
+  def reset!
+    @all = nil
+  end
+
   def generate_subclasses
     IssueCustomField.all.map do |field|
       class_name = class_name_for field.name
diff --git a/init.rb b/init.rb
index 2e01539bef..d528a18ed5 100644
--- a/init.rb
+++ b/init.rb
@@ -3,6 +3,11 @@ require 'redmine'
 # Hooks
 require 'view_projects_show_sidebar_bottom_hook'
 
+Dispatcher.to_prepare do
+  # Model Patches
+  require_dependency 'reporting_issue_custom_field_patch'
+end
+
 Redmine::Plugin.register :redmine_reporting do
   name 'Reporting Plugin'
   author 'Konstantin Haase, Philipp Tessenow @ finnlabs'
diff --git a/lib/reporting_issue_custom_field_patch.rb b/lib/reporting_issue_custom_field_patch.rb
new file mode 100644
index 0000000000..2a09b6c603
--- /dev/null
+++ b/lib/reporting_issue_custom_field_patch.rb
@@ -0,0 +1,26 @@
+module ReportingIssueCustomFieldPatch
+  def self.included(base) # :nodoc:
+    base.send(:include, InstanceMethods)
+
+    # Same as typing in the class
+    base.class_eval do
+      unloadable
+      after_save :generate_custom_field_filters
+      after_save :generate_custom_field_group_bys
+    end
+  end
+
+  module InstanceMethods
+    def generate_custom_field_filters
+      CostQuery::Filter.reset!
+      CostQuery::Filter::CustomFieldEntries.reset!
+    end
+
+    def generate_custom_field_group_bys
+      CostQuery::GroupBy.reset!
+      CostQuery::GroupBy::CustomFieldEntries.reset!
+    end
+  end
+end
+
+IssueCustomField.send(:include, ReportingIssueCustomFieldPatch)