diff --git a/Gemfile b/Gemfile
index e210be466..37f48fab8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -120,6 +120,8 @@ group :development do
 end
 
 group :development, :test do
+  gem 'sorbet'
+  gem 'sorbet-runtime'
   gem 'graphql-schema_comparator'
   gem 'mina', require: false # Deploy
   gem 'pry-byebug' # Call 'byebug' anywhere in the code to stop execution and get a debugger console
diff --git a/Gemfile.lock b/Gemfile.lock
index b91f5e62a..5737b95dc 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -677,6 +677,18 @@ GEM
       tilt (~> 2.0)
     skylight (5.0.1)
       activesupport (>= 5.2.0)
+    sorbet (0.5.9827)
+      sorbet-static (= 0.5.9827)
+    sorbet-runtime (0.5.9827)
+    sorbet-static (0.5.9827-universal-darwin-14)
+    sorbet-static (0.5.9827-universal-darwin-15)
+    sorbet-static (0.5.9827-universal-darwin-16)
+    sorbet-static (0.5.9827-universal-darwin-17)
+    sorbet-static (0.5.9827-universal-darwin-18)
+    sorbet-static (0.5.9827-universal-darwin-19)
+    sorbet-static (0.5.9827-universal-darwin-20)
+    sorbet-static (0.5.9827-universal-darwin-21)
+    sorbet-static (0.5.9827-x86_64-linux)
     spreadsheet_architect (4.1.0)
       axlsx_styler (>= 1.0.0, < 2)
       caxlsx (>= 2.0.2, < 4)
@@ -874,6 +886,8 @@ DEPENDENCIES
   sib-api-v3-sdk
   simple_xlsx_reader
   skylight
+  sorbet
+  sorbet-runtime
   spreadsheet_architect
   spring
   spring-commands-rspec
diff --git a/app/models/dossier.rb b/app/models/dossier.rb
index fbef6d1a3..f5991efc0 100644
--- a/app/models/dossier.rb
+++ b/app/models/dossier.rb
@@ -1,3 +1,4 @@
+# typed: true
 # == Schema Information
 #
 # Table name: dossiers
@@ -38,6 +39,7 @@
 #  user_id                                            :integer
 #
 class Dossier < ApplicationRecord
+  extend T::Sig
   self.ignored_columns = [:en_construction_conservation_extension]
   include DossierFilteringConcern
   include DossierRebaseConcern
@@ -233,8 +235,8 @@ class Dossier < ApplicationRecord
   scope :en_instruction,              -> { not_archived.state_en_instruction }
   scope :termine,                     -> { not_archived.state_termine }
 
+  sig { params(args: DateTime).returns(T.untyped) }
   scope :processed_in_month, -> (date) do
-    date = date.to_datetime
     state_termine
       .joins(:traitements)
       .where(traitements: { processed_at: date.beginning_of_month..date.end_of_month })
diff --git a/sorbet/config b/sorbet/config
new file mode 100644
index 000000000..534118e61
--- /dev/null
+++ b/sorbet/config
@@ -0,0 +1,3 @@
+--dir
+.
+--ignore=/vendor/bundle
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index b58e5553d..e52754382 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -13,6 +13,7 @@ require 'rspec/rails'
 require 'axe-rspec'
 require 'devise'
 require 'shoulda-matchers'
+require 'sorbet-runtime'
 
 # Requires supporting ruby files with custom matchers and macros, etc, in
 # spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are