diff --git a/addons/website_slides/data/slide_user_demo.xml b/addons/website_slides/data/slide_user_demo.xml
index 80d87842323..cc8b45a6219 100644
--- a/addons/website_slides/data/slide_user_demo.xml
+++ b/addons/website_slides/data/slide_user_demo.xml
@@ -2,6 +2,15 @@
 <odoo><data noupdate="1">
     <!-- CHANNEL 0: Basics of Gardening -->
     <!-- ================================================== -->
+    <!-- Note that admin is already member due to auto subscribe -->
+    <record id="slide_channel_0_partner_demo" model="slide.channel.partner">
+        <field name="channel_id" ref="website_slides.slide_channel_demo_0_gard_0"/>
+        <field name="partner_id" ref="base.partner_demo"/>
+    </record>
+    <record id="slide_channel_0_partner_demo_portal" model="slide.channel.partner">
+        <field name="channel_id" ref="website_slides.slide_channel_demo_0_gard_0"/>
+        <field name="partner_id" ref="base.partner_demo_portal"/>
+    </record>
     <record id="slide_slide_0_0_partner_admin" model="slide.slide.partner">
         <field name="slide_id" ref="website_slides.slide_slide_demo_0_0"/>
         <field name="partner_id" ref="base.partner_admin"/>
@@ -78,6 +87,15 @@
 
     <!-- CHANNEL 1: Taking care of Trees -->
     <!-- ================================================== -->
+    <!-- Note that admin is already member due to auto subscribe -->
+    <record id="slide_channel_1_partner_demo" model="slide.channel.partner">
+        <field name="channel_id" ref="website_slides.slide_channel_demo_1_gard1"/>
+        <field name="partner_id" ref="base.partner_demo"/>
+    </record>
+    <record id="slide_channel_1_partner_demo_portal" model="slide.channel.partner">
+        <field name="channel_id" ref="website_slides.slide_channel_demo_1_gard1"/>
+        <field name="partner_id" ref="base.partner_demo_portal"/>
+    </record>
     <record id="slide_slide_1_0_partner_admin" model="slide.slide.partner">
     	<field name="slide_id" ref="website_slides.slide_slide_demo_1_0"/>
     	<field name="partner_id" ref="base.partner_admin"/>
@@ -187,6 +205,10 @@
 
     <!-- CHANNEL 2: Trees, Wood and Garden -->
     <!-- ================================================== -->
+    <record id="slide_channel_2_partner_admin" model="slide.channel.partner">
+        <field name="channel_id" ref="website_slides.slide_channel_demo_2_gard2"/>
+        <field name="partner_id" ref="base.partner_admin"/>
+    </record>
     <record id="slide_slide_2_0_partner_admin" model="slide.slide.partner">
         <field name="slide_id" ref="website_slides.slide_slide_demo_2_0"/>
         <field name="partner_id" ref="base.partner_admin"/>
@@ -199,10 +221,7 @@
         <field name="partner_id" ref="base.partner_admin"/>
         <field name="vote">1</field>
     </record>
-    <record id="slide_channel_2_partner_demo" model="slide.channel.partner">
-        <field name="channel_id" ref="website_slides.slide_channel_demo_2_gard2"/>
-        <field name="partner_id" ref="base.partner_demo"/>
-    </record>
+    <!-- note that partner demo is already member of slide_channel_demo_2_gard2 due to auto subscribe -->
     <record id="slide_slide_2_0_partner_demo" model="slide.slide.partner">
         <field name="slide_id" ref="website_slides.slide_slide_demo_2_0"/>
         <field name="partner_id" ref="base.partner_demo"/>
diff --git a/addons/website_slides/models/slide_channel.py b/addons/website_slides/models/slide_channel.py
index fdda9b34b2d..402222f0e8b 100644
--- a/addons/website_slides/models/slide_channel.py
+++ b/addons/website_slides/models/slide_channel.py
@@ -34,6 +34,13 @@ class ChannelUsersRelation(models.Model):
     channel_enroll = fields.Selection(related='channel_id.enroll')
     channel_website_id = fields.Many2one('website', string='Website', related='channel_id.website_id')
 
+    _sql_constraints = [
+        ('channel_partner_uniq',
+         'unique(channel_id, partner_id)',
+         'A partner membership to a channel must be unique!'
+        ),
+    ]
+
     def _recompute_completion(self):
         read_group_res = self.env['slide.slide.partner'].sudo().read_group(
             ['&', '&', ('channel_id', 'in', self.mapped('channel_id').ids),
diff --git a/addons/website_slides/models/slide_slide.py b/addons/website_slides/models/slide_slide.py
index 74ada83cee0..7386cfc597b 100644
--- a/addons/website_slides/models/slide_slide.py
+++ b/addons/website_slides/models/slide_slide.py
@@ -36,6 +36,13 @@ class SlidePartnerRelation(models.Model):
     completed = fields.Boolean('Completed')
     quiz_attempts_count = fields.Integer('Quiz attempts count', default=0)
 
+    _sql_constraints = [
+        ('slide_partner_uniq',
+         'unique(slide_id, partner_id)',
+         'A partner membership to a slide must be unique!'
+        )
+    ]
+
     @api.model_create_multi
     def create(self, vals_list):
         res = super().create(vals_list)