diff --git a/src/addons/mod/glossary/pages/edit/edit.ts b/src/addons/mod/glossary/pages/edit/edit.ts
index 950751961..4c2aa09fe 100644
--- a/src/addons/mod/glossary/pages/edit/edit.ts
+++ b/src/addons/mod/glossary/pages/edit/edit.ts
@@ -286,9 +286,9 @@ abstract class AddonModGlossaryFormHandler {
      * Upload attachments online.
      *
      * @param glossary Glossary.
-     * @returns Uploaded attachments item id.
+     * @returns Uploaded attachments item id, undefined if nothing to upload or change.
      */
-    protected async uploadAttachments(glossary: AddonModGlossaryGlossary): Promise<number> {
+    protected async uploadAttachments(glossary: AddonModGlossaryGlossary): Promise<number | undefined> {
         const data = this.page.data;
         const itemId = await CoreFileUploader.uploadOrReuploadFiles(
             data.attachments,
@@ -643,10 +643,7 @@ class AddonModGlossaryOnlineFormHandler extends AddonModGlossaryFormHandler {
             data.fullmatch = this.entry.fullmatch;
         }
 
-        // Treat offline attachments if any.
-        if (this.entry.attachments) {
-            data.attachments = this.entry.attachments;
-        }
+        data.attachments = (this.entry.attachments ?? []).slice();
 
         this.page.originalData = {
             concept: data.concept,
@@ -677,11 +674,7 @@ class AddonModGlossaryOnlineFormHandler extends AddonModGlossaryFormHandler {
         const definition = CoreText.formatHtmlLines(data.definition);
 
         // Upload attachments, if any.
-        let attachmentsId: number | undefined = undefined;
-
-        if (data.attachments.length) {
-            attachmentsId = await this.uploadAttachments(glossary);
-        }
+        const attachmentsId = await this.uploadAttachments();
 
         // Save entry data.
         await AddonModGlossary.updateEntry(glossary.id, this.entry.id, data.concept, definition, options, attachmentsId);
@@ -694,6 +687,31 @@ class AddonModGlossaryOnlineFormHandler extends AddonModGlossaryFormHandler {
         return true;
     }
 
+    /**
+     * Upload attachments online.
+     *
+     * @returns Uploaded attachments item id, undefined if nothing to upload or change.
+     */
+    protected async uploadAttachments(): Promise<number | undefined> {
+        const data = this.page.data;
+
+        if (!CoreFileUploader.areFileListDifferent(data.attachments, this.entry.attachments ?? [])) {
+            return;
+        }
+
+        const { attachmentsid: attachmentsId } = await AddonModGlossary.prepareEntryForEdition(this.entry.id);
+
+        const removedFiles = CoreFileUploader.getFilesToDelete(this.entry.attachments ?? [], data.attachments);
+
+        if (removedFiles.length) {
+            await CoreFileUploader.deleteDraftFiles(attachmentsId, removedFiles);
+        }
+
+        await CoreFileUploader.uploadFiles(attachmentsId, data.attachments);
+
+        return attachmentsId;
+    }
+
 }
 
 /**
diff --git a/src/addons/mod/glossary/services/glossary.ts b/src/addons/mod/glossary/services/glossary.ts
index a9c12cf1a..715ee9575 100644
--- a/src/addons/mod/glossary/services/glossary.ts
+++ b/src/addons/mod/glossary/services/glossary.ts
@@ -626,6 +626,7 @@ export class AddonModGlossaryProvider {
      *
      * @param siteId Site id.
      * @returns Whether the site can update entries.
+     * @since 3.10
      */
     async canUpdateEntries(siteId?: string): Promise<boolean> {
         const site = await CoreSites.getSite(siteId);
@@ -1097,6 +1098,26 @@ export class AddonModGlossaryProvider {
         await site.getDb().insertRecord(ENTRIES_TABLE_NAME, entry);
     }
 
+    /**
+     * Prepare entry for edition.
+     *
+     * @param entryId Entry ID.
+     * @param siteId Site ID.
+     * @returns Data of prepared area.
+     */
+    async prepareEntryForEdition(
+        entryId: number,
+        siteId?: string,
+    ): Promise<AddonModGlossaryPrepareEntryForEditionWSResponse> {
+        const site = await CoreSites.getSite(siteId);
+
+        const params: AddonModGlossaryPrepareEntryForEditionWSParams = {
+            entryid: entryId,
+        };
+
+        return await site.write('mod_glossary_prepare_entry_for_edition', params);
+    }
+
 }
 
 export const AddonModGlossary = makeSingleton(AddonModGlossaryProvider);
@@ -1435,6 +1456,31 @@ export type AddonModGlossaryViewEntryWSParams = {
     id: number; // Glossary entry ID.
 };
 
+/**
+ * Params of mod_glossary_prepare_entry_for_edition WS.
+ */
+type AddonModGlossaryPrepareEntryForEditionWSParams = {
+    entryid: number; // Glossary entry id to update.
+};
+
+/**
+ * Data returned by mod_glossary_prepare_entry_for_edition WS.
+ */
+export type AddonModGlossaryPrepareEntryForEditionWSResponse = {
+    inlineattachmentsid: number; // Draft item id for the text editor.
+    attachmentsid: number; // Draft item id for the file manager.
+    areas: { // File areas including options.
+        area: string; // File area name.
+        options: { // Draft file area options.
+            name: string; // Name of option.
+            value: string; // Value of option.
+        }[];
+    }[];
+    aliases: string[];
+    categories: number[];
+    warnings?: CoreWSExternalWarning[];
+};
+
 /**
  * Options to pass to add entry.
  */