diff --git a/addons/web/models/models.py b/addons/web/models/models.py
index b1a5908fdf0..b68f0b52e10 100644
--- a/addons/web/models/models.py
+++ b/addons/web/models/models.py
@@ -213,6 +213,9 @@ class Base(models.AbstractModel):
                         group_by_value, format=DISPLAY_DATE_FORMATS[group_by_modifier],
                         locale=locale)
 
+            if field_type == 'many2many' and isinstance(group_by_value, list):
+                group_by_value = str(tuple(group_by_value)) or False
+
             record_values[group_by] = group_by_value
             record_values['__count'] = 1
 
diff --git a/addons/web/tests/test_read_progress_bar.py b/addons/web/tests/test_read_progress_bar.py
index c4d1a5b0e75..2c265d9797e 100644
--- a/addons/web/tests/test_read_progress_bar.py
+++ b/addons/web/tests/test_read_progress_bar.py
@@ -11,6 +11,20 @@ class TestReadProgressBar(common.TransactionCase):
         super(TestReadProgressBar, self).setUp()
         self.Model = self.env['res.partner']
 
+    def test_read_progress_bar_m2m(self):
+        """ Test that read_progress_bar works with m2m field grouping """
+        progressbar = {
+            'field': 'type',
+            'colors': {
+                'contact': 'success', 'private': 'danger', 'other': 'muted',
+            }
+        }
+        result = self.env['res.partner'].read_progress_bar([], 'category_id', progressbar)
+        # check that it works when grouping by m2m field
+        self.assertTrue(result)
+        # check the null group
+        self.assertIn('False', result)
+
     def test_week_grouping(self):
         """The labels associated to each record in read_progress_bar should match
         the ones from read_group, even in edge cases like en_US locale on sundays