diff --git a/app/models/project.rb b/app/models/project.rb
index 878b4c0ca..8a79ed674 100644
--- a/app/models/project.rb
+++ b/app/models/project.rb
@@ -76,7 +76,7 @@ class Project < ActiveRecord::Base
   validates_length_of :homepage, :maximum => 255
   validates_length_of :identifier, :in => 1..IDENTIFIER_MAX_LENGTH
   # donwcase letters, digits, dashes but not digits only
-  validates_format_of :identifier, :with => /^(?!\d+$)[a-z0-9\-]*$/, :if => Proc.new { |p| p.identifier_changed? }
+  validates_format_of :identifier, :with => /^(?!\d+$)[a-z0-9\-_]*$/, :if => Proc.new { |p| p.identifier_changed? }
   # reserved words
   validates_exclusion_of :identifier, :in => %w( new )
 
diff --git a/config/locales/en-GB.yml b/config/locales/en-GB.yml
index 66a6e0bed..9a5b8565a 100644
--- a/config/locales/en-GB.yml
+++ b/config/locales/en-GB.yml
@@ -879,7 +879,7 @@ en-GB:
   text_tip_issue_begin_day: task beginning this day
   text_tip_issue_end_day: task ending this day
   text_tip_issue_begin_end_day: task beginning and ending this day
-  text_project_identifier_info: 'Only lower case letters (a-z), numbers and dashes are allowed.<br />Once saved, the identifier cannot be changed.'
+  text_project_identifier_info: 'Only lower case letters (a-z), numbers, dashes and underscores are allowed.<br />Once saved, the identifier cannot be changed.'
   text_caracters_maximum: "%{count} characters maximum."
   text_caracters_minimum: "Must be at least %{count} characters long."
   text_length_between: "Length between %{min} and %{max} characters."
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 6ac30adec..e9f160db1 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -915,7 +915,7 @@ en:
   text_tip_issue_begin_day: issue beginning this day
   text_tip_issue_end_day: issue ending this day
   text_tip_issue_begin_end_day: issue beginning and ending this day
-  text_project_identifier_info: 'Only lower case letters (a-z), numbers and dashes are allowed.<br />Once saved, the identifier cannot be changed.'
+  text_project_identifier_info: 'Only lower case letters (a-z), numbers, dashes and underscores are allowed.<br />Once saved, the identifier cannot be changed.'
   text_caracters_maximum: "%{count} characters maximum."
   text_caracters_minimum: "Must be at least %{count} characters long."
   text_length_between: "Length between %{min} and %{max} characters."
diff --git a/config/locales/fr.yml b/config/locales/fr.yml
index 562a488a7..e2029b591 100644
--- a/config/locales/fr.yml
+++ b/config/locales/fr.yml
@@ -882,7 +882,7 @@ fr:
   text_tip_issue_begin_day: tâche commençant ce jour
   text_tip_issue_end_day: tâche finissant ce jour
   text_tip_issue_begin_end_day: tâche commençant et finissant ce jour
-  text_project_identifier_info: 'Seuls les lettres minuscules (a-z), chiffres et tirets sont autorisés.<br />Un fois sauvegardé, l''identifiant ne pourra plus être modifié.'
+  text_project_identifier_info: 'Seuls les lettres minuscules (a-z), chiffres, tirets et underscore sont autorisés.<br />Un fois sauvegardé, l''identifiant ne pourra plus être modifié.'
   text_caracters_maximum: "%{count} caractères maximum."
   text_caracters_minimum: "%{count} caractères minimum."
   text_length_between: "Longueur comprise entre %{min} et %{max} caractères."
diff --git a/test/unit/project_test.rb b/test/unit/project_test.rb
index b3fd3de24..2901b6efa 100644
--- a/test/unit/project_test.rb
+++ b/test/unit/project_test.rb
@@ -119,6 +119,7 @@ class ProjectTest < ActiveSupport::TestCase
     to_test = {"abc" => true,
                "ab12" => true,
                "ab-12" => true,
+               "ab_12" => true,
                "12" => false,
                "new" => false}