diff --git a/mappers/commerce_product_reference.inc b/mappers/commerce_product_reference.inc
index 136764b..b4b9bf9 100644
--- a/mappers/commerce_product_reference.inc
+++ b/mappers/commerce_product_reference.inc
@@ -15,17 +15,21 @@ function _commerce_product_reference_feeds_processor_targets_alter(&$targets, $e
     $info = field_info_field($name);
     if ($info['type'] == 'commerce_product_reference') {
       if (array_key_exists('product_id', $info['columns'])) {
+        // Real target is modified in order to keep the older values from the
+        // field of the entity to support accumulative imports.
+        // See http://drupal.org/node/1188994
+
         $targets[$name . ":product_id"] = array(
           'name' => $instance['label'] . ': Product ID',
           'callback' => 'commerce_product_reference_feeds_set_target',
           'description' => t('The product id for the @name field. NOTE: use this feature with care, products ids are usually assigned by Drupal.', array('@name' => $instance['label'])),
-          'real_target' => $name,
+          'real_target' => 'commerce-' . $name,
         );
         $targets[$name . ":sku"] = array(
           'name' => $instance['label'] . ': SKU',
           'callback' => 'commerce_product_reference_feeds_set_target',
           'description' => t('The SKU reference for the @name field. NOTE: the product entity needs to exist.', array('@name' => $instance['label'])),
-          'real_target' => $name,
+          'real_target' => 'commerce-' . $name,
         );
       }
     }
@@ -39,7 +43,7 @@ function _commerce_product_reference_feeds_processor_targets_alter(&$targets, $e
  * user has decided to map to and $value contains the value of the feed item
  * element the user has picked as a source.
  */
-function commerce_product_reference_feeds_set_target($source, $entity, $target, $value) {
+function commerce_product_reference_feeds_set_target(FeedsSource $source, $entity, $target, $value) {
   if (empty($value)) {
     return;
   }
@@ -54,22 +58,63 @@ function commerce_product_reference_feeds_set_target($source, $entity, $target,
   $info = field_info_field($field_name);
   $field = isset($entity->$field_name) ? $entity->$field_name : array();
 
-  // Iterate over all values.
-  foreach ($value as $i => $v) {
-    if (!is_array($v) && !is_object($v)) {
-      if ($sub_field == 'product_id') {
-        $field[LANGUAGE_NONE][$i]['product_id'] = $v;
-      }
-      elseif ($sub_field == 'sku') {
-        if ($product = commerce_product_load_by_sku($v)) {
-          $field[LANGUAGE_NONE][$i]['product_id'] = $product->product_id;
-        } else {
-          drupal_set_message(t('A product with SKU %sku could not be found. Please check that the product exists or import it first.', array('%sku' => $v)), 'error');
+  // If we're replacing the existing content, we'd want to keep the existing
+  // field content and update it accordingly.
+  // Also, if the field is empty, we map the values the usual way.
+  if ($source->importer->config['processor']['config']['update_existing'] == FEEDS_UPDATE_EXISTING && !empty($field) && count($field[LANGUAGE_NONE])) {
+    $i = count($field[LANGUAGE_NONE]);
+
+    foreach ($value as $v) {
+      if (!is_array($v) && !is_object($v)) {
+        if (strstr($target, 'product_id')) {
+          $product_id = $v;
         }
+        elseif (strstr($target, 'sku')) {
+          if ($product = commerce_product_load_by_sku($v)) {
+            $product_id = $product->product_id;
+          }
+          else {
+            drupal_set_message(t('A product with SKU %sku could not be found. Please check that the product exists or import it first.', array('%sku' => $v)), 'error');
+          }
+        }
+        if ($product_id) {
+          $delta = $i;
+          // If there are already some elements in the field, we search for it to reuse them.
+          foreach($field[LANGUAGE_NONE] as $key=>$id) {
+            if ($id['product_id'] == $product_id) {
+              $delta = $key;
+              break;
+            }
+          }
+          $field[LANGUAGE_NONE][$delta]['product_id'] = $product_id;
+        }
+      }
+      if ($info['cardinality'] == 1) {
+        break;
       }
+      $i++;
     }
-    if ($info['cardinality'] == 1) {
-      break;
+  }
+  else {
+    // If we're not updating, we're replacing or creating so a normal behavior
+    // is expected.
+    // Iterate over all values.
+    foreach ($value as $i => $v) {
+      if (!is_array($v) && !is_object($v)) {
+        if ($sub_field == 'product_id') {
+          $field[LANGUAGE_NONE][$i]['product_id'] = $v;
+        }
+        elseif ($sub_field == 'sku') {
+          if ($product = commerce_product_load_by_sku($v)) {
+            $field[LANGUAGE_NONE][$i]['product_id'] = $product->product_id;
+          } else {
+            drupal_set_message(t('A product with SKU %sku could not be found. Please check that the product exists or import it first.', array('%sku' => $v)), 'error');
+          }
+        }
+      }
+      if ($info['cardinality'] == 1) {
+        break;
+      }
     }
   }