diff --git a/ihatemoney/forms.py b/ihatemoney/forms.py
index de9004d5..c818b75b 100644
--- a/ihatemoney/forms.py
+++ b/ihatemoney/forms.py
@@ -2,7 +2,7 @@ from flask_wtf.form import FlaskForm
 from wtforms.fields.core import SelectField, SelectMultipleField
 from wtforms.fields.html5 import DateField, DecimalField
 from wtforms.fields.simple import PasswordField, SubmitField, TextAreaField, StringField
-from wtforms.validators import Email, Required, ValidationError, EqualTo
+from wtforms.validators import Email, Required, ValidationError, EqualTo, NumberRange
 from flask_babel import lazy_gettext as _
 from flask import request
 from werkzeug.security import generate_password_hash
@@ -149,9 +149,11 @@ class BillForm(FlaskForm):
 
 
 class MemberForm(FlaskForm):
-
     name = StringField(_("Name"), validators=[Required()])
-    weight = CommaDecimalField(_("Weight"), default=1)
+
+    wieght_validators = [NumberRange(min=0.1, message=_("Weights should be positive"))]
+    weight = CommaDecimalField(_("Weight"), default=1,
+                               validators=weight_validators)
     submit = SubmitField(_("Add"))
 
     def __init__(self, project, edit=False, *args, **kwargs):
diff --git a/ihatemoney/messages.pot b/ihatemoney/messages.pot
index bc8a8f39..a47740e1 100644
--- a/ihatemoney/messages.pot
+++ b/ihatemoney/messages.pot
@@ -74,6 +74,9 @@ msgstr ""
 msgid "Weight"
 msgstr ""
 
+msgid "Weights should be positive"
+msgstr ""
+
 msgid "Add"
 msgstr ""
 
diff --git a/ihatemoney/tests/tests.py b/ihatemoney/tests/tests.py
index fd72a8da..6fbd6f93 100644
--- a/ihatemoney/tests/tests.py
+++ b/ihatemoney/tests/tests.py
@@ -619,6 +619,18 @@ class BudgetTestCase(IhatemoneyTestCase):
         resp = self.client.get("/raclette/")
         self.assertNotIn('extra-info', resp.data.decode('utf-8'))
 
+    def test_negative_weight(self):
+        self.post_project("raclette")
+
+        # Add one user and edit it to have a negative share
+        self.client.post("/raclette/members/add", data={'name': 'alexis'})
+        resp = self.client.post("/raclette/members/1/edit", data={'name': 'alexis', 'weight': -1})
+
+        # An error should be generated, and its weight should still be 1.
+        self.assertIn('<p class="alert alert-danger">', resp.data.decode('utf-8'))
+        self.assertEqual(len(models.Project.query.get('raclette').members), 1)
+        self.assertEqual(models.Project.query.get('raclette').members[0].weight, 1)
+
     def test_rounding(self):
         self.post_project("raclette")
 
diff --git a/ihatemoney/translations/fr/LC_MESSAGES/messages.po b/ihatemoney/translations/fr/LC_MESSAGES/messages.po
index ccab28b1..05dc6cf6 100644
--- a/ihatemoney/translations/fr/LC_MESSAGES/messages.po
+++ b/ihatemoney/translations/fr/LC_MESSAGES/messages.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2018-07-16 23:26+0200\n"
+"POT-Creation-Date: 2018-08-05 16:21+0200\n"
 "PO-Revision-Date: 2018-05-15 22:00+0200\n"
 "Last-Translator: Adrien CLERC <>\n"
 "Language: fr\n"
@@ -16,7 +16,7 @@ msgstr ""
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=utf-8\n"
 "Content-Transfer-Encoding: 8bit\n"
-"Generated-By: Babel 2.5.3\n"
+"Generated-By: Babel 2.6.0\n"
 
 msgid "Project name"
 msgstr "Nom de projet"
@@ -98,6 +98,9 @@ msgstr "Nom"
 msgid "Weight"
 msgstr "Parts"
 
+msgid "Weights should be positive"
+msgstr "Les parts doivent être positives"
+
 msgid "Add"
 msgstr "Ajouter"
 
@@ -488,4 +491,3 @@ msgstr "Solde"
 
 #~ msgid "Invite"
 #~ msgstr "Invitez"
-