BUG: UDUnits-style powers must not be followed by a letter

src/metpy/units.py

@@ -56,7 +56,7 @@ def _fix_udunits_div(string):
 
 # Fix UDUNITS-style powers, percent signs, and ill-defined units
 _UDUNIT_POWER = re.compile(r'(?<=[A-Za-z\)])(?![A-Za-z\)])'
-                           r'(?<![0-9\-][eE])(?<![0-9\-])(?=[0-9\-])')
+                           r'(?<![0-9\-][eE])(?<![0-9\-])(?=-?[0-9]+([ )]|$))')
 _unit_preprocessors = [_fix_udunits_powers, lambda string: string.replace('%', 'percent'),
                        _fix_udunits_div]
 

tests/units/test_units.py

@@ -11,7 +11,7 @@
 from metpy.testing import (assert_almost_equal, assert_array_almost_equal, assert_array_equal,
                            assert_nan)
 from metpy.units import (check_units, concatenate, is_quantity,
-                         pandas_dataframe_to_unit_arrays, units)
+                         pandas_dataframe_to_unit_arrays, UndefinedUnitError, units)
 
 
 def test_concatenate():
@@ -231,9 +231,19 @@ def test_percent_units():
             marks=pytest.mark.xfail(reason='hgrecco/pint#1485')
         ),
         ('(J kg-1)(m s-1)(-1)', units.m ** 3 / units.s ** 3),
-        ('/s', units.s ** -1)
+        ('/s', units.s ** -1),
+        ('feet_H2O', units.kg / units.m / units.s ** 2)
     )
 )
 def test_udunits_power_syntax(unit_str, pint_unit):
     """Test that UDUNITS style powers are properly parsed and interpreted."""
     assert units(unit_str).to_base_units().units == pint_unit
+
+
+def test_unsupported_udunits_power_fails():
+    """Test that removing the spaces between factors causes parsing to fail.
+
+    UDUnits does not support this either.
+    """
+    with pytest.raises(UndefinedUnitError):
+        assert units('m2s-2').to_base_units.units == units.m ** 2 / units.s ** 2