diff --git a/mod/forum/amd/build/repository.min.js b/mod/forum/amd/build/repository.min.js
index 16de8615ee1..40df235d3ae 100644
--- a/mod/forum/amd/build/repository.min.js
+++ b/mod/forum/amd/build/repository.min.js
@@ -1 +1 @@
-define(["core/ajax"],function(a){var b=function(b,c,d){var e={methodname:"mod_forum_set_subscription_state",args:{forumid:b,discussionid:c,targetstate:d}};return a.call([e])[0]},c=function(b,c,d,e,f,g){var h={methodname:"mod_forum_add_discussion_post",args:{postid:b,message:d,messageformat:e,subject:c,options:[{name:"private",value:f},{name:"tohtml",value:g}]}};return a.call([h])[0]},d=function(b,c,d){var e={methodname:"mod_forum_toggle_favourite_state",args:{discussionid:c,targetstate:d}};return a.call([e])[0]},e=function(b,c,d){var e={methodname:"mod_forum_set_lock_state",args:{forumid:b,discussionid:c,targetstate:d}};return a.call([e])[0]},f=function(b,c,d){var e={methodname:"mod_forum_set_pin_state",args:{discussionid:c,targetstate:d}};return a.call([e])[0]};return{setDiscussionSubscriptionState:b,addDiscussionPost:c,setDiscussionLockState:e,setFavouriteDiscussionState:d,setPinDiscussionState:f}});
\ No newline at end of file
+define(["core/ajax"],function(a){var b=function(b,c,d){var e={methodname:"mod_forum_set_subscription_state",args:{forumid:b,discussionid:c,targetstate:d}};return a.call([e])[0]},c=function(b,c,d,e,f,g){var h={methodname:"mod_forum_add_discussion_post",args:{postid:b,message:d,messageformat:e,subject:c,options:[{name:"private",value:f},{name:"topreferredformat",value:g}]}};return a.call([h])[0]},d=function(b,c,d){var e={methodname:"mod_forum_toggle_favourite_state",args:{discussionid:c,targetstate:d}};return a.call([e])[0]},e=function(b,c,d){var e={methodname:"mod_forum_set_lock_state",args:{forumid:b,discussionid:c,targetstate:d}};return a.call([e])[0]},f=function(b,c,d){var e={methodname:"mod_forum_set_pin_state",args:{discussionid:c,targetstate:d}};return a.call([e])[0]};return{setDiscussionSubscriptionState:b,addDiscussionPost:c,setDiscussionLockState:e,setFavouriteDiscussionState:d,setPinDiscussionState:f}});
\ No newline at end of file
diff --git a/mod/forum/amd/src/inpage_reply.js b/mod/forum/amd/src/inpage_reply.js
index 7b9edd3b20f..014e64669ce 100644
--- a/mod/forum/amd/src/inpage_reply.js
+++ b/mod/forum/amd/src/inpage_reply.js
@@ -94,7 +94,7 @@ define([
             // In the future, other formats should be supported, letting users to use their preferred editor and format.
             var messageformat = CONTENT_FORMATS.MOODLE;
             // The message post will be converted from messageformat to FORMAT_HTML.
-            var tohtml = true;
+            var topreferredformat = true;
             var postid = form.elements.reply.value;
             var subject = form.elements.subject.value;
             var currentRoot = submitButton.parents(Selectors.post.forumContent);
@@ -106,7 +106,7 @@ define([
                 showSubmitButtonLoadingIcon(submitButton);
                 allButtons.prop('disabled', true);
 
-                Repository.addDiscussionPost(postid, subject, message, messageformat, isprivatereply, tohtml)
+                Repository.addDiscussionPost(postid, subject, message, messageformat, isprivatereply, topreferredformat)
                     .then(function(context) {
                         var message = context.messages.reduce(function(carry, message) {
                             if (message.type == 'success') {
diff --git a/mod/forum/amd/src/repository.js b/mod/forum/amd/src/repository.js
index e63fb48387a..1e8e29d694d 100644
--- a/mod/forum/amd/src/repository.js
+++ b/mod/forum/amd/src/repository.js
@@ -43,7 +43,7 @@ define(['core/ajax'], function(Ajax) {
         return Ajax.call([request])[0];
     };
 
-    var addDiscussionPost = function(postid, subject, message, messageformat, isprivatereply, tohtml) {
+    var addDiscussionPost = function(postid, subject, message, messageformat, isprivatereply, topreferredformat) {
         var request = {
             methodname: 'mod_forum_add_discussion_post',
             args: {
@@ -55,8 +55,8 @@ define(['core/ajax'], function(Ajax) {
                     name: "private",
                     value: isprivatereply,
                 }, {
-                    name: "tohtml",
-                    value: tohtml,
+                    name: "topreferredformat",
+                    value: topreferredformat,
                 }]
             }
         };
diff --git a/mod/forum/externallib.php b/mod/forum/externallib.php
index 6f5b6613d09..37f09d7b9dd 100644
--- a/mod/forum/externallib.php
+++ b/mod/forum/externallib.php
@@ -1188,7 +1188,7 @@ class mod_forum_external extends external_api {
                                         private (bool); make this reply private to the author of the parent post, default to false.
                                         inlineattachmentsid              (int); the draft file area id for inline attachments
                                         attachmentsid       (int); the draft file area id for attachments
-                                        tohtml (bool); convert the message & messageformat to FORMAT_HTML, defaults to false
+                                        topreferredformat (bool); convert the message & messageformat to FORMAT_HTML, defaults to false
                             '),
                             'value' => new external_value(PARAM_RAW, 'the value of the option,
                                                             this param is validated in the external function.'
@@ -1263,7 +1263,7 @@ class mod_forum_external extends external_api {
             'private'             => false,
             'inlineattachmentsid' => 0,
             'attachmentsid' => null,
-            'tohtml'        => false
+            'topreferredformat'   => false
         );
         foreach ($params['options'] as $option) {
             $name = trim($option['name']);
@@ -1284,7 +1284,7 @@ class mod_forum_external extends external_api {
                         $value = 0;
                     }
                     break;
-                case 'tohtml':
+                case 'topreferredformat':
                     $value = clean_param($option['value'], PARAM_BOOL);
                     break;
                 default:
@@ -1300,10 +1300,15 @@ class mod_forum_external extends external_api {
         $thresholdwarning = forum_check_throttling($forumrecord, $cm);
         forum_check_blocking_threshold($thresholdwarning);
 
-        // If we want to force a conversion to HTML, let's do it now.
-        if ($options['tohtml'] && $params['messageformat'] != FORMAT_HTML) {
-            $params['message'] = format_text($params['message'], $params['messageformat'], ['context' => $context]);
-            $params['messageformat'] = FORMAT_HTML;
+        // If we want to force a conversion to the preferred format, let's do it now.
+        if ($options['topreferredformat']) {
+            // We always are going to honor the preferred format. We are creating a new post.
+            $preferredformat = editors_get_preferred_format();
+            // If the post is not HTML and the preferred format is HTML, convert to it.
+            if ($params['messageformat'] != FORMAT_HTML and $preferredformat == FORMAT_HTML) {
+                $params['message'] = format_text($params['message'], $params['messageformat'], ['context' => $context]);
+            }
+            $params['messageformat'] = $preferredformat;
         }
 
         // Create the post.
diff --git a/mod/forum/tests/externallib_test.php b/mod/forum/tests/externallib_test.php
index 35696addc04..5e903acbee5 100644
--- a/mod/forum/tests/externallib_test.php
+++ b/mod/forum/tests/externallib_test.php
@@ -1601,9 +1601,10 @@ class mod_forum_external_testcase extends externallib_advanced_testcase {
             $this->assertEquals($format, $dbformat);
         }
 
-        // Now let's try the 'tohtml' option. That should end with the content
-        // transformed and the format being FORMAT_HTML always.
-        $options = [['name' => 'tohtml', 'value' => true]];
+        // Now let's try the 'topreferredformat' option. That should end with the content
+        // transformed and the format being FORMAT_HTML (when, like in this case,  user preferred
+        // format is HTML, inferred from editor in preferences).
+        $options = [['name' => 'topreferredformat', 'value' => true]];
         $createdpost = mod_forum_external::add_discussion_post($discussion->firstpost,
             'interesting subject', 'with some https://example.com link', $options, FORMAT_MOODLE);
         $createdpost = external_api::clean_returnvalue(mod_forum_external::add_discussion_post_returns(), $createdpost);
diff --git a/mod/forum/upgrade.txt b/mod/forum/upgrade.txt
index 50f0f2a263c..6f5c9b9df41 100644
--- a/mod/forum/upgrade.txt
+++ b/mod/forum/upgrade.txt
@@ -14,7 +14,7 @@ information provided here is intended especially for developers.
   * New external function mod_forum_external::get_forum_discussions returns a list of forum discussions optionally sorted and paginated.
   * External function mod_forum_external::get_forum_discussions_paginated has been deprecated.
     Use mod_forum_external::get_forum_discussions instead.
-  * External function mod_forum_external::add_discussion_post() has a new 'messageformat' param to be able to handle other formats different from FORMAT_HTML (that continues being the default one). Also a new 'tohtml' option enables the automatic conversion between any format and FORMAT_HTML before contents are saved.
+  * External function mod_forum_external::add_discussion_post() has a new 'messageformat' param to be able to handle other formats different from FORMAT_HTML (that continues being the default one). Also a new 'topreferredformat' option enables the automatic conversion between any format and the preferred format (given the editor preference) before contents are saved.
 
 === 3.6 ===