diff --git a/app/models/lessons_validator.rb b/app/models/lessons_validator.rb
index 1c068c4..6685995 100644
--- a/app/models/lessons_validator.rb
+++ b/app/models/lessons_validator.rb
@@ -7,6 +7,7 @@ def validate_each(record, attribute, value)
 
     check_correct_class(record, attribute, value)
     check_unique_refs(record, attribute, value)
+    check_unique_title(record, attribute, value)
   end
 
   def check_correct_class(record, attribute, value)
@@ -26,4 +27,16 @@ def check_unique_refs(record, attribute, value)
       non_unique_refs.each { |ref| record.errors.add(attribute, "(#{lesson.title}) segment ref #{ref} is not unique") }
     end
   end
+
+  def check_unique_title(record, attribute, value)
+    return unless value.is_a?(Array)
+
+    value.each do |lesson|
+      title_counts = Hash.new(0)
+      lesson.segments.each { |segment| title_counts[segment.title] += 1 }
+      non_unique_titles = title_counts.select { |_, count| count > 1 }.keys
+
+      non_unique_titles.each { |title| record.errors.add(attribute, "(#{lesson}) segment title #{title} is not unique") }
+    end
+  end
 end