diff --git a/.rubocop.yml b/.rubocop.yml
index 8cf0c86e..c9f7c91c 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -342,3 +342,6 @@ Style/CollectionQuerying:
   Enabled: true
 Lint/AmbiguousRange:
   Enabled: true
+
+Style/OneClassPerFile:
+  Enabled: false
diff --git a/lib/sequent/core/active_projectors_event_publisher.rb b/lib/sequent/core/active_projectors_event_publisher.rb
index c64dbb24..1e7c6b57 100644
--- a/lib/sequent/core/active_projectors_event_publisher.rb
+++ b/lib/sequent/core/active_projectors_event_publisher.rb
@@ -30,7 +30,7 @@ def process_events(event_handlers, ...)
 
       def ensure_no_unknown_active_projectors!(event_handlers)
         registered_projectors = event_handlers
-          .select { |x| x.is_a?(Projector) }
+          .grep(Projector)
           .map { |x| x.class.name }
         activated_projectors = Projectors.projector_states
           .values
diff --git a/lib/sequent/core/event_store.rb b/lib/sequent/core/event_store.rb
index 705c967a..68d6f95d 100644
--- a/lib/sequent/core/event_store.rb
+++ b/lib/sequent/core/event_store.rb
@@ -267,7 +267,7 @@ def event_streams_enumerator(aggregate_type: nil, group_size: 100)
       end
 
       def update_unique_keys(event_streams)
-        fail ArgumentError, 'array of stream records expected' unless event_streams.all? { |x| x.is_a?(EventStream) }
+        fail ArgumentError, 'array of stream records expected' unless event_streams.all?(EventStream)
 
         call_procedure(connection, 'update_unique_keys', [event_streams.to_json])
       rescue ActiveRecord::RecordNotUnique => e
diff --git a/lib/sequent/core/helpers/unique_keys.rb b/lib/sequent/core/helpers/unique_keys.rb
index 194a9fe6..76fca1be 100644
--- a/lib/sequent/core/helpers/unique_keys.rb
+++ b/lib/sequent/core/helpers/unique_keys.rb
@@ -33,7 +33,7 @@ module ClassMethods
           # ```
           def unique_key(scope, *attributes, **kwargs)
             fail ArgumentError, "'#{scope}' is not a symbol" unless scope.is_a?(Symbol)
-            fail ArgumentError, 'attributes must be symbols' unless attributes.all? { |attr| attr.is_a?(Symbol) }
+            fail ArgumentError, 'attributes must be symbols' unless attributes.all?(Symbol)
 
             @unique_key_definitions ||= {}
 
diff --git a/lib/sequent/core/persistors/replay_optimized_postgres_persistor.rb b/lib/sequent/core/persistors/replay_optimized_postgres_persistor.rb
index 900c71b7..6d2dc1d9 100644
--- a/lib/sequent/core/persistors/replay_optimized_postgres_persistor.rb
+++ b/lib/sequent/core/persistors/replay_optimized_postgres_persistor.rb
@@ -82,7 +82,7 @@ def hash
 
         def struct_cache
           @struct_cache ||= Hash.new do |hash, record_class|
-            struct_class = Struct.new(*record_class.column_names.map(&:to_sym), keyword_init: true) do
+            struct_class = Struct.new(*record_class.column_names.map(&:to_sym)) do
               include InMemoryStruct
             end
             hash[record_class] = struct_class
diff --git a/lib/sequent/core/projector.rb b/lib/sequent/core/projector.rb
index 473befa5..b68461aa 100644
--- a/lib/sequent/core/projector.rb
+++ b/lib/sequent/core/projector.rb
@@ -28,7 +28,7 @@ def version = projector_version || Sequent.migrations_class&.version || 1
       end
 
       def self.projectors
-        Sequent.configuration.event_handlers.select { |x| x.is_a? Migratable }.map(&:class)
+        Sequent.configuration.event_handlers.grep(Migratable).map(&:class)
       end
 
       def self.included(host_class)
@@ -187,7 +187,7 @@ def ensure_record_class_supported!(record_class)
       def ensure_valid!
         if self.class.managed_tables.nil?
           fail <<~EOS.chomp
-            A Projector must manage at least one table. Did you forget to add `managed_tables` to #{self.class.name}?
+            A Projector must manage at least one table. Did you forget to add `managed_tables` to #{self.class}?
           EOS
         end
       end
diff --git a/spec/lib/sequent/core/projector_spec.rb b/spec/lib/sequent/core/projector_spec.rb
index 658f9697..0591a659 100644
--- a/spec/lib/sequent/core/projector_spec.rb
+++ b/spec/lib/sequent/core/projector_spec.rb
@@ -39,12 +39,13 @@ class MyOtherProjectorTable
   context 'versioning' do
     let(:parent_projector_class) do
       Class.new(Sequent::Core::Projector) do
+        manages_no_tables
         self.version = 3
       end
     end
 
     it 'should default to 1 if not specified' do
-      projector_class = Class.new(Sequent::Core::Projector)
+      projector_class = Class.new(Sequent::Core::Projector) { manages_no_tables }
 
       expect(projector_class.version).to eq(1)
     end