diff --git a/admin-dev/tabs/AdminCustomers.php b/admin-dev/tabs/AdminCustomers.php
index 8894e9a78..1c8783c5b 100644
--- a/admin-dev/tabs/AdminCustomers.php
+++ b/admin-dev/tabs/AdminCustomers.php
@@ -798,7 +798,7 @@ class AdminCustomers extends AdminTab
 					echo '<option value="'.(int)($group['id_group']).'"'.($group['id_group'] == $obj->id_default_group ? ' selected="selected"' : '').'>'.htmlentities($group['name'], ENT_NOQUOTES, 'utf-8').'</option>';
 				echo '
 					</select>
-					<p>'.$this->l('Apply non-cumulative rules (e.g., price, display method, reduction)').'</p>
+					<div class="hintGroup">'.$this->l('The group will be as applied by default.').'</div>
 				</div>
 				<label>'.$this->l('Groups:').' </label>
 				<div class="margin-form">';
diff --git a/admin-dev/tabs/AdminGroups.php b/admin-dev/tabs/AdminGroups.php
index 70b27773e..9b72edc2e 100644
--- a/admin-dev/tabs/AdminGroups.php
+++ b/admin-dev/tabs/AdminGroups.php
@@ -93,7 +93,9 @@ class AdminGroups extends AdminTab
 				<div class="margin-form">';
 			if ($groupReductions)
 			{
-				echo '<table>
+				
+				echo '
+					<table>
 						<tr>
 							<th>'.$this->l('Category').'</th>
 							<th>'.$this->l('Value').'</th>
@@ -141,6 +143,7 @@ class AdminGroups extends AdminTab
 			<form action="'.self::$currentIndex.'&update'.$this->table.'&id_group='.$obj->id.'&token='.$this->token.'" method="post" class="width3">
 				<input type="hidden" name="id_'.$this->table.'" value="'.$obj->id.'" />
 				<fieldset><legend><img src="../img/admin/tab-groups.gif" />'.$this->l('New group discount').'</legend>
+					<div class="hintGroup">'.$this->l('Beware the reduction applied to a category does not stack with the overall reduction but replaces. The group is automatically added to the category.').'</div>
 					<label>'.$this->l('Category:').' </label>
 					<div class="margin-form">
 						<select name="id_category">';
@@ -151,7 +154,7 @@ class AdminGroups extends AdminTab
 					</div>
 					<label>'.$this->l('Discount (in %):').' </label>
 					<div class="margin-form">
-						<input type="text" name="reduction" value="" /><sup>*</sup>
+						<input type="text" name="reductionByCategory" value="" /><sup>*</sup>
 					</div>
 					<div class="clear">&nbsp;</div>
 					<div class="margin-form">
@@ -306,12 +309,17 @@ class AdminGroups extends AdminTab
 				$groupReduction = new GroupReduction();
 				if (!$id_category = Tools::getValue('id_category') OR !Validate::isUnsignedId($id_category))
 					$this->_errors[] = Tools::displayError('Wrong category ID');
-				elseif (!$reduction = Tools::getValue('reduction') OR !Validate::isPrice($reduction))
+				elseif (!$reduction = Tools::getValue('reductionByCategory') OR !Validate::isPrice($reduction))
 					$this->_errors[] = Tools::displayError('Invalid reduction (must be a percentage)');
-				elseif (GroupReduction::doesExist((int)($obj->id), $id_category))
+				elseif (Tools::getValue('reductionByCategory') > 100 OR Tools::getValue('reductionByCategory') < 0)
+					$this->_errors[] = Tools::displayError('Reduction value is incorrect');
+				elseif (GroupReduction::doesExist((int)($obj->id), $id_category)){
 					$this->_errors[] = Tools::displayError('A reduction already exists for this category.');
+				}
 				else
 				{
+					$category = new Category((int)$id_category);
+					$category->addGroupsIfNoExist(Tools::getValue('id_group'));
 					$groupReduction->id_category = (int)($id_category);
 					$groupReduction->id_group = (int)($obj->id);
 					$groupReduction->reduction = (float)($reduction) / 100;
@@ -338,7 +346,9 @@ class AdminGroups extends AdminTab
 					{
 						foreach ($id_group_reductions AS $key => $id_group_reduction)
 							if (!Validate::isUnsignedId($id_group_reductions[$key]) OR !Validate::isPrice($reductions[$key]))
-								$this->_errors[] = Tools::displayError();
+								$this->_errors[] = Tools::displayError('Invalid reduction (must be a percentage)');
+							elseif ($reductions[$key] > 100 OR $reductions[$key] < 0)
+								$this->_errors[] = Tools::displayError('Reduction value is incorrect');
 							else
 							{
 								$groupReduction = new GroupReduction((int)($id_group_reductions[$key]));
diff --git a/classes/Category.php b/classes/Category.php
index 1ba579849..fb6e23512 100644
--- a/classes/Category.php
+++ b/classes/Category.php
@@ -849,6 +849,18 @@ class CategoryCore extends ObjectModel
 			$groups[] = $group['id_group'];
 		return $groups;
 	}
+	
+	public function addGroupsIfNoExist($id_group)
+	{
+		$groups = $this->getGroups();
+		p($groups);
+		foreach($groups as $group){
+			if($group != $id_group)
+				return false;
+			else
+				$this->addGroups(array((int)($id_group)));
+		}
+	}
 
 	/**
 	 * checkAccess return true if id_customer is in a group allowed to see this category.
diff --git a/css/admin.css b/css/admin.css
index 71b7804e6..d0ed3bedf 100644
--- a/css/admin.css
+++ b/css/admin.css
@@ -762,6 +762,16 @@ div.hint {
 	position: relative;
 }
 
+.hintGroup{
+	position: relative;
+	margin-top: 10px;
+	margin-bottom: 10px;
+	border: 1px solid #50B0EC;
+	padding: 8px 6px 8px 40px;
+	color: #383838;
+	background: #DDE9F7 url(../img/admin/help2.png) no-repeat 6px 5px;
+}
+
 
 /* The pointer image is added by using another span */
 .hint .hint-pointer {
diff --git a/translations/fr/admin.php b/translations/fr/admin.php
index 414adfd0e..aa3b0fada 100644
--- a/translations/fr/admin.php
+++ b/translations/fr/admin.php
@@ -727,7 +727,7 @@ $_LANGADM['AdminCustomers8d218b952c9ef571cd270aaef8f849d1'] = 'Autoriser ou non
 $_LANGADM['AdminCustomerscca344269d726c206f3d3894c85cae5a'] = 'Client abonné à la newsletter';
 $_LANGADM['AdminCustomers5ed5ce582affef97f07fa474c6751302'] = 'Client acceptant de recevoir des publicités';
 $_LANGADM['AdminCustomers8d177b48ffca1fb18c3bfd1e8c0eb645'] = 'Groupe par défaut:';
-$_LANGADM['AdminCustomers7aea94ad2dc662cb934bc6746775fd3f'] = 'Le groupe à partir du quelle s\'appliquent les règles non cumulatives (par exemple, la méthode d\'affichage des prix, réduction)';
+$_LANGADM['AdminCustomersbf935f3541fafe3c2a68d2c52b0856b5'] = 'Le groupe par défaut est le groupe qui appliquera les règles non cumulatives (par exemple, la méthode d\'affichage des prix, réduction)';
 $_LANGADM['AdminCustomers8783bc7ae2b9e8d93a2bc15150aaefa8'] = 'Groupes :';
 $_LANGADM['AdminCustomersc6155aaecccf794cd2a00fcc35898022'] = 'Nom du groupe';
 $_LANGADM['AdminCustomers3cf21846659529ae741430ff2ddf287f'] = 'Cochez tous les groupes auxquels appartient le membre';
@@ -1020,6 +1020,7 @@ $_LANGADM['AdminGroups817b35caca2afa11b6c1efc428315470'] = 'Groupe de boutiques
 $_LANGADM['AdminGroups38fb7d24e0d60a048f540ecb18e13376'] = 'Enregistrer';
 $_LANGADM['AdminGroups19f823c6453c2b1ffd09cb715214813d'] = 'Champs requis';
 $_LANGADM['AdminGroupsc53a3dc4f27d93e065c2c5be5a78b74f'] = 'Nouvelle réduction de groupe';
+$_LANGADM['AdminGroupsf3301519f560b65be8d8e67336df5b07'] = 'Attention, la réduction appliqué à une catégorie ne se cumule pas avec la réduction global mais la remplace. Le groupe est automatiquement ajoutée à la catégorie.';
 $_LANGADM['AdminGroups56a8a9eb05f9014da51a4f9b57322ac7'] = 'Catégorie :';
 $_LANGADM['AdminGroups60c4a9a7f56f6b9669f84977ebd0f93d'] = 'Seuls les produits qui ont cette catégorie par défaut seront ajoutés';
 $_LANGADM['AdminGroups567183b8b1122180690be51cc6df2b74'] = 'Réduction (en %) :';