qgis - Adding field to PostGIS Layer with PyQGIS

I'm having trouble adding a field to a PostGIS table using PyQGIS. Here's my code:

from PyQt4.QtCore import QVariant
from qgis.core import *

inLayer = iface.activeLayer()
provider = inLayer.dataProvider()

# add field

field = QgsField('test_field', QVariant.String)
inLayer.startEditing()
provider.addAttributes([field])
inLayer.updateFields()

# commit
inLayer.commitChanges()

The commit fails and the PostGIS log shows an error:

2015-10-27T08:13:28 1 Erroneous query: ALTER TABLE "received"."env" ADD COLUMN "test_field" returned 7 [ERROR: syntax error at end of input

LINE 1: ALTER TABLE "received"."env" ADD COLUMN "test_field"

Seems the call to PostGIS fails to include the column type. Is this a bug, or am I going about this the wrong way?