Request works with sqlite not with Postgres

Hello,

The following request works in my dev django project (sqlite) by not in production with postgres

out: >>> Questionnaire.objects.filter(site_id=1).annotate(moyenne=Avg('chrono__temps')).values('title','moyenne')

The errors :

 out: Traceback (most recent call last):
 out:   File "<console>", line 1, in <module>
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/query.py", line 234, in __repr__
 out:     data = list(self[:REPR_OUTPUT_SIZE + 1])
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/query.py", line 258, in __iter__
 out:     self._fetch_all()
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/query.py", line 1074, in _fetch_all
 out:     self._result_cache = list(self.iterator())
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/query.py", line 112, in __iter__
 out:     for row in compiler.results_iter():
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 808, in results_iter
 out:     row = self.apply_converters(row, converters)
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 792, in apply_converters
 out:     value = converter(value, expression, self.connection, self.query.context)
 out:   File "/home/mimi/.virtualenvs/atmav2/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 283, in convert_value
 out:     return float(value)
 out: TypeError: float() argument must be a string or a number

Thank you for your help.

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