diff --git a/survey_input_attachment/models/survey_question.py b/survey_input_attachment/models/survey_question.py
index 9c16b41..6f2d02a 100644
--- a/survey_input_attachment/models/survey_question.py
+++ b/survey_input_attachment/models/survey_question.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
-from odoo import models, fields, _
+from odoo import models, fields, api, _
+from werkzeug.datastructures import FileStorage
 
 TYPES = [
     ('free_text', _('Multiple Lines Text Box')),
@@ -18,3 +19,15 @@ class SurveyQuestion(models.Model):
 
     # question_attachment = fields.Binary(string="Joined attachment")
     type = fields.Selection(selection=TYPES)
+
+    @api.multi
+    def validate_upload_file(self, post, answer_tag):
+        self.ensure_one()
+        errors = {}
+        # Empty answer to mandatory question
+        if self.constr_mandatory and not isinstance(post[answer_tag], FileStorage):
+            errors.update({answer_tag: self.constr_error_msg})
+        # Bad file type
+        if isinstance(post[answer_tag], FileStorage) and post[answer_tag].content_type != 'application/pdf' and 'image/' not in post[answer_tag].content_type:
+            errors.update({answer_tag: _("The file you joined is not an image nor a PDF file.")})
+        return errors
diff --git a/survey_input_attachment/models/survey_user_input_line.py b/survey_input_attachment/models/survey_user_input_line.py
index 2b44adc..d028325 100644
--- a/survey_input_attachment/models/survey_user_input_line.py
+++ b/survey_input_attachment/models/survey_user_input_line.py
@@ -33,11 +33,13 @@ class SurveyUserInputLine(models.Model):
             'survey_id': question.survey_id.id,
             'skipped': False
         }
+        file = False
+        # import ipdb; ipdb.set_trace()
         if question.constr_mandatory:
-            file = base64.encodebytes(post[answer_tag].read())
+                file = base64.encodebytes(post[answer_tag].read())
         else:
-            file = base64.encodebytes(post[answer_tag].read()) if post[answer_tag] else None
-        if answer_tag in post:
+            file = base64.encodebytes(post[answer_tag].read()) if not isinstance(post[answer_tag], str) else None
+        if answer_tag in post and not isinstance(post[answer_tag], str):
             vals.update({
                 'answer_type': 'upload_file',
                 'file': file,