diff --git a/db/install.xml b/db/install.xml
index 6291f86..38050b1 100755
--- a/db/install.xml
+++ b/db/install.xml
@@ -91,6 +91,7 @@
       <INDEXES>
         <INDEX NAME="authorid" UNIQUE="false" FIELDS="authorid"/>
         <INDEX NAME="conversationid" UNIQUE="false" FIELDS="conversationid"/>
+        <INDEX NAME="dialogueid" UNIQUE="false" FIELDS="dialogueid"/>
       </INDEXES>
     </TABLE>
     <TABLE NAME="dialogue_flags" COMMENT="Flags set against a dialogue, conversation or message e.g read">
diff --git a/db/upgrade.php b/db/upgrade.php
index 01022ad..415bdc6 100644
--- a/db/upgrade.php
+++ b/db/upgrade.php
@@ -30,5 +30,23 @@
  * @return bool
  */
 function xmldb_dialogue_upgrade($oldversion) {
+    global $DB;
+
+    $dbman = $DB->get_manager();
+
+    if ($oldversion < 2024120900) {
+        // Define index dialogueid (not unique) to be added to dialogue_messages.
+        $table = new xmldb_table('dialogue_messages');
+        $index = new xmldb_index('dialogueid', XMLDB_INDEX_NOTUNIQUE, ['dialogueid']);
+
+        // Conditionally launch add index userid.
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+
+        // savepoint reached.
+        upgrade_mod_savepoint(true, 2024120900, 'dialogue');
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index 063cade..dbbe610 100644
--- a/version.php
+++ b/version.php
@@ -23,8 +23,8 @@
  */
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2024100901;
-$plugin->release   = 2024100901;
+$plugin->version   = 2024120900;
+$plugin->release   = 2024120900;
 $plugin->requires  = 2022112805;  // Requires 4.1 or higher.
 $plugin->component = 'mod_dialogue';    // Full name of the plugin (used for diagnostics).
 $plugin->maturity  = MATURITY_STABLE;    // This version's maturity level.