diff --git a/admin/batch_manager_global.php b/admin/batch_manager_global.php
index fce6087f5..2dacd1182 100644
--- a/admin/batch_manager_global.php
+++ b/admin/batch_manager_global.php
@@ -458,6 +458,7 @@ usort($prefilters, 'UC_name_compare');
 
 $template->assign(
   array(
+    'conf_checksum_compute_blocksize' => $conf['checksum_compute_blocksize'],
     'prefilters' => $prefilters,
     'filter' => $_SESSION['bulk_manager_filter'],
     'selection' => $collection,
diff --git a/admin/themes/default/js/batchManagerGlobal.js b/admin/themes/default/js/batchManagerGlobal.js
index da8163f6a..89a261cb1 100644
--- a/admin/themes/default/js/batchManagerGlobal.js
+++ b/admin/themes/default/js/batchManagerGlobal.js
@@ -420,7 +420,7 @@ jQuery('#sync_md5sum').click(function(e) {
 
   var addBlockSize = Math.min(
     Number((jQuery('#md5sum_to_add').data('origin') / 2).toFixed()),
-    1000
+    conf.checksum_compute_blocksize
   );
   add_md5sum_block(addBlockSize);
 
diff --git a/admin/themes/default/template/batch_manager_global.tpl b/admin/themes/default/template/batch_manager_global.tpl
index 0ab1708fd..5134c8137 100644
--- a/admin/themes/default/template/batch_manager_global.tpl
+++ b/admin/themes/default/template/batch_manager_global.tpl
@@ -26,6 +26,10 @@ var lang = {
 	AreYouSure: "{'Are you sure?'|translate|escape:'javascript'}"
 };
 
+var conf = {
+  checksum_compute_blocksize: {$conf_checksum_compute_blocksize},
+};
+
 jQuery(document).ready(function() {
 
   jQuery('.help-popin').colorbox({ width:"500px" });
diff --git a/include/config_default.inc.php b/include/config_default.inc.php
index 7e8fe0506..67269846b 100644
--- a/include/config_default.inc.php
+++ b/include/config_default.inc.php
@@ -841,6 +841,9 @@ $conf['batch_manager_images_per_page_global'] = 20;
 // unit mode. Must be among values {5, 10, 50}
 $conf['batch_manager_images_per_page_unit'] = 5;
 
+// how many missing md5sum should Piwigo compute at once.
+$conf['checksum_compute_blocksize'] = 50;
+
 // +-----------------------------------------------------------------------+
 // |                                 log                                   |
 // +-----------------------------------------------------------------------+