diff --git a/moldesign/_tests/helpers.py b/moldesign/_tests/helpers.py
index 269244f..b210754 100644
--- a/moldesign/_tests/helpers.py
+++ b/moldesign/_tests/helpers.py
@@ -32,7 +32,7 @@ def _make_mol_with_n_hydrogens(n):
     return mdt.Molecule([mdt.Atom('H') for i in xrange(n)])
 
 
-class ZeroEnergy(mdt.models.EnergyModelBase):
+class ZeroEnergy(mdt.models.base.EnergyModelBase):
     """ All 0, all the time
     """
     def prep(self):
diff --git a/moldesign/compute/configuration.py b/moldesign/compute/configuration.py
index dec22ab..e77a7db 100644
--- a/moldesign/compute/configuration.py
+++ b/moldesign/compute/configuration.py
@@ -92,7 +92,7 @@
                                 default_python_image=None,
                                 default_docker_host='unix://var/run/docker.sock',
                                 default_docker_machine='default',
-                                default_version_tag='0.7.2')
+                                default_version_tag='0.7.3')
 
 DEF_CONFIG = CONFIG_DEFAULTS.copy()
 """ dict: default configuration to be written to moldesign.yml if it doesn't exist
diff --git a/moldesign/molecules/bonds.py b/moldesign/molecules/bonds.py
index 01ee940..c0460b9 100644
--- a/moldesign/molecules/bonds.py
+++ b/moldesign/molecules/bonds.py
@@ -27,7 +27,8 @@ class Bond(object):
 
     Notes:
         Comparisons and hashes involving bonds will return True if the atoms involved in the bonds
-            are the same. Bond orders are not compared.
+        are the same. Bond orders are not compared.
+
         These objects are used to represent and pass bond data only - they are not used for storage.
 
     Attributes:
diff --git a/moldesign/units/quantity.py b/moldesign/units/quantity.py
index 643ff05..431b1ad 100644
--- a/moldesign/units/quantity.py
+++ b/moldesign/units/quantity.py
@@ -17,6 +17,7 @@
 import operator
 import copy
 from os.path import join, abspath, dirname
+import numbers
 
 import numpy as np
 from pint import UnitRegistry, set_application_registry, DimensionalityError
@@ -95,7 +96,9 @@ def __setitem__(self, key, value):
             if not hasattr(value, 'value_in'):  # deal with missing `value_in` method
                 if self.dimensionless:  # case 1: this is OK if self is dimensionless
                     self.magnitude[key] = value
-                else:  # case 2: User tried to pass a number without units
+                elif not isinstance(value, numbers.Number):  # case 2: this is not a number
+                    raise TypeError('"%s" is not a valid numeric value' % value)
+                else:  # case 3: wrong units
                     raise DimensionalityError(self.units, ureg.dimensionless)
             else:  # case 3: attribute error is unrelated to this
                 raise