diff --git a/plugins/sources/mssql.inc b/plugins/sources/mssql.inc
index f8d2b1d..60484e9 100644
--- a/plugins/sources/mssql.inc
+++ b/plugins/sources/mssql.inc
@@ -160,7 +160,17 @@ class MigrateSourceMSSQL extends MigrateSource {
         $keys[0] . ' IN (' . implode(',', $this->idList) . ')', $this->query);
     }
     else {
-      if (isset($this->highwaterField['name']) && $highwater = $this->activeMigration->getHighwater()) {
+      $add_highwater_condition = TRUE;
+      // If there are any needs_update rows, we need to skip adding the
+      // highwater condition because it will interfere with the updates.
+      $count_needs_update = db_query('SELECT COUNT(*) FROM {' .
+        $this->activeMap->getQualifiedMapTable() . '} WHERE needs_update = 1')
+        ->fetchField();
+      if ($count_needs_update > 0) {
+        $add_highwater_condition = FALSE;
+      }
+
+      if ($add_highwater_condition && isset($this->highwaterField['name']) && $highwater = $this->activeMigration->getHighwater()) {
         if (empty($this->highwaterField['alias'])) {
           $highwater_name = $this->highwaterField['name'];
         }