diff --git a/app/models/event_schedule.rb b/app/models/event_schedule.rb
index cb630acd..fbf5de69 100644
--- a/app/models/event_schedule.rb
+++ b/app/models/event_schedule.rb
@@ -11,6 +11,8 @@ class EventSchedule < ActiveRecord::Base
   validates :start_time, presence: true
   validates :event, uniqueness: { scope: :schedule }
 
+  validate :not_overlapping
+
   scope :confirmed, -> { joins(:event).where('state = ?', 'confirmed') }
   scope :canceled, -> { joins(:event).where('state = ?', 'canceled') }
   scope :withdrawn, -> { joins(:event).where('state = ?', 'withdrawn') }
@@ -36,4 +38,15 @@ class EventSchedule < ActiveRecord::Base
   def conference_id
     schedule.program.conference_id
   end
+
+  def not_overlapping
+    if room
+      room.event_schedules.where(schedule: schedule).where.not(id: id).each do |e|
+        if (e.start_time <= start_time && e.end_time > start_time) || (e.end_time >= end_time && e.start_time < end_time) || (e.start_time > start_time && e.start_time < end_time)
+          errors.add(:event, "can't be scheduled at the same time than other event in the same room")
+          break
+        end
+      end
+    end
+  end
 end
diff --git a/spec/models/event_schedule_spec.rb b/spec/models/event_schedule_spec.rb
index 28b04ddf..33ce4edb 100644
--- a/spec/models/event_schedule_spec.rb
+++ b/spec/models/event_schedule_spec.rb
@@ -17,5 +17,32 @@ describe EventSchedule do
     it { is_expected.to validate_presence_of(:event) }
     it { is_expected.to validate_presence_of(:room) }
     it { is_expected.to validate_presence_of(:start_time) }
+
+    describe '#not_overlapping' do
+      let!(:event) { create(:event, event_type: create(:event_type, length: 60)) }
+      let!(:event2) { create(:event, event_type: create(:event_type, length: 30), program: event.program) }
+      let!(:schedule) { create(:schedule, program: event.program) }
+      let!(:room) { create(:room, venue: create(:venue, conference: event.program.conference)) }
+      let!(:event_schedule) { create(:event_schedule, schedule: schedule, event: event, room: room, start_time: event.program.conference.start_date.tomorrow.to_time + 60.minutes) }
+
+      describe "can't be scheduled at the same time than other event in the same room" do
+        it 'case 1' do
+          expect(build(:event_schedule, schedule: schedule, event: event2, room: room, start_time: event_schedule.start_time - 15.minutes)).to_not be_valid
+        end
+
+        it 'case 2' do
+          expect(build(:event_schedule, schedule: schedule, event: event2, room: room, start_time: event_schedule.start_time + 45.minutes)).to_not be_valid
+        end
+
+        it 'case 3' do
+          expect(build(:event_schedule, schedule: schedule, event: event2, room: room, start_time: event_schedule.start_time + 15.minutes)).to_not be_valid
+        end
+
+        it 'case 4' do
+          event2.event_type = create(:event_type, length: 120)
+          expect(build(:event_schedule, schedule: schedule, event: event2, room: room, start_time: event_schedule.start_time - 30.minutes)).to_not be_valid
+        end
+      end
+    end
   end
 end