diff --git a/odoo/addons/base/models/res_lang.py b/odoo/addons/base/models/res_lang.py
index 16e6850e3ef..1f47c64b4ab 100644
--- a/odoo/addons/base/models/res_lang.py
+++ b/odoo/addons/base/models/res_lang.py
@@ -81,6 +81,23 @@ class Lang(models.Model):
                                             'Please refer to the list of allowed directives, '
                                             'displayed when you edit a language.'))
 
+    @api.onchange('time_format', 'date_format')
+    def _onchange_format(self):
+        warning = {
+            'warning': {
+                'title': _("Using 24-hour clock format with AM/PM can cause issues."),
+                'message': _("Changing to 12-hour clock format instead."),
+                'type': 'notification'
+            }
+        }
+        for lang in self:
+            if lang.date_format and "%H" in lang.date_format and "%p" in lang.date_format:
+                lang.date_format = lang.date_format.replace("%H", "%I")
+                return warning
+            if lang.time_format and "%H" in lang.time_format and "%p" in lang.time_format:
+                lang.time_format = lang.time_format.replace("%H", "%I")
+                return warning
+
     @api.constrains('grouping')
     def _check_grouping(self):
         warning = _('The Separator Format should be like [,n] where 0 < n :starting from Unit digit. '