diff --git a/openerp/models.py b/openerp/models.py
index 3d9b1850f9d..40c04992287 100644
--- a/openerp/models.py
+++ b/openerp/models.py
@@ -5782,7 +5782,18 @@ class BaseModel(object):
                 if 'domain' in method_res:
                     result.setdefault('domain', {}).update(method_res['domain'])
                 if 'warning' in method_res:
-                    result['warning'] = method_res['warning']
+                    if 'warning' in result:
+                        # Concatenate multiple warnings
+                        warning = result['warning']
+                        warning['message'] = '\n\n'.join(filter(None, [
+                            warning.get('title'),
+                            warning.get('message'),
+                            method_res['warning'].get('title'),
+                            method_res['warning'].get('message')
+                        ]))
+                        warning['title'] = _('Warnings')
+                    else:
+                        result['warning'] = method_res['warning']
             return
 
         # onchange V7
@@ -5823,8 +5834,18 @@ class BaseModel(object):
             if 'domain' in method_res:
                 result.setdefault('domain', {}).update(method_res['domain'])
             if 'warning' in method_res:
-                result['warning'] = method_res['warning']
-
+                if 'warning' in result:
+                    # Concatenate multiple warnings
+                    warning = result['warning']
+                    warning['message'] = '\n\n'.join(filter(None, [
+                        warning.get('title'),
+                        warning.get('message'),
+                        method_res['warning'].get('title'),
+                        method_res['warning'].get('message')
+                    ]))
+                    warning['title'] = _('Warnings')
+                else:
+                    result['warning'] = method_res['warning']
     @api.multi
     def onchange(self, values, field_name, field_onchange):
         """ Perform an onchange on the given field.