diff --git a/app/models/event.rb b/app/models/event.rb
index b28b8b0ba..8007f6a4e 100644
--- a/app/models/event.rb
+++ b/app/models/event.rb
@@ -13,8 +13,7 @@ class Event < ActiveRecord::Base
   attr_accessor :recurrence, :recurrence_end_at
 
   after_create :event_recurrence
-  before_save :set_nb_free_places
-  before_update :update_nb_free_places, if: :nb_total_places_changed?
+  before_save :update_nb_free_places
 
   def name
     title
@@ -33,6 +32,10 @@ class Event < ActiveRecord::Base
     end
   end
 
+  def reservations
+    Reservation.where(reservable: self)
+  end
+
   private
   def event_recurrence
     if recurrence.present? and recurrence != 'none'
@@ -79,16 +82,12 @@ class Event < ActiveRecord::Base
     end
   end
 
-  def set_nb_free_places
-    if nb_free_places.nil?
-      self.nb_free_places = nb_total_places
-    end
-  end
-
   def update_nb_free_places
-    unless nb_total_places_was.nil? or nb_total_places.nil?
-      diff = nb_total_places - nb_total_places_was
-      self.nb_free_places += diff
+    if nb_total_places.nil?
+      self.nb_free_places = nil
+    else
+      reserved_places = reservations.map{|r| r.nb_reserve_places + r.nb_reserve_reduced_places}.inject(0){|sum, t| sum + t }
+      self.nb_free_places = (nb_total_places - reserved_places)
     end
   end
 end