diff --git a/gemd/__version__.py b/gemd/__version__.py
index edc60b3..b6d2a0c 100644
--- a/gemd/__version__.py
+++ b/gemd/__version__.py
@@ -1 +1 @@
-__version__ = "2.1.6"
+__version__ = "2.1.7"
diff --git a/gemd/units/citrine_en.txt b/gemd/units/citrine_en.txt
index ea19497..1bbf774 100644
--- a/gemd/units/citrine_en.txt
+++ b/gemd/units/citrine_en.txt
@@ -1,6 +1,6 @@
 # Citrine customized units input file for Pint, based explicitly on the Pint defaults as
-# included release 0.20 (https://github.com/hgrecco/pint/releases/tag/0.20).  The Pint Authors hold
-# copyright and are documented in https://github.com/hgrecco/pint/blob/0.20/AUTHORS.
+# included release 0.23 (https://github.com/hgrecco/pint/releases/tag/0.23).  The Pint Authors hold
+# copyright and are documented in https://github.com/hgrecco/pint/blob/0.23/AUTHORS.
 #
 # The original copyright statement for the constants file reads:
 #
@@ -106,6 +106,8 @@
 #### PREFIXES ####
 
 # decimal prefixes
+quecto- = 1e-30 = q-
+ronto- = 1e-27 = r-
 yocto- = 1e-24 = y-
 zepto- = 1e-21 = z-
 atto- =  1e-18 = a-
@@ -128,6 +130,8 @@ peta- =  1e15  = P-
 exa- =   1e18  = E-
 zetta- = 1e21  = Z-
 yotta- = 1e24  = Y-
+ronna- = 1e27 = R-
+quetta- = 1e30 = Q-
 
 # binary_prefixes
 kibi- = 2**10 = Ki-
@@ -189,9 +193,14 @@ byte = 8 * bit = B = octet = Byte = Octet
 # byte = 8 * bit = _ = octet
 ## NOTE: B (byte) symbol can conflict with Bell
 
+# Ratios
+percent = 0.01 = % = pct
+permille = 0.001 = ‰ = per_thousand
+ppm = 1e-6 = per_million
+
 # Length
 angstrom = 1e-10 * meter = Å = ångström = Angstrom = Ångstrom = Å
-micron = micrometer = µ = Micron
+micron = micrometer = µ = μ = Micron
 fermi = femtometer = fm = Fermi
 light_year = speed_of_light * julian_year = ly = lightyear = Light_Year = Lightyear
 astronomical_unit = 149597870700 * meter = au = Astronomical_Unit  # since Aug 2012
@@ -468,6 +477,10 @@ atomic_unit_of_electric_field = e * k_C / a_0 ** 2 = a_u_electric_field
 # Electric displacement field
 [electric_displacement_field] = [charge] / [area]
 
+# Reduced electric field
+[reduced_electric_field] = [electric_field] * [area]
+townsend =  1e-21 * V * m^2 = Td = Townsend
+
 # Resistance
 [resistance] = [electric_potential] / [current]
 ohm = volt / ampere = Ω = Ohm
@@ -707,10 +720,10 @@ neper = 1 ; logbase: 2.71828182845904523536028747135266249775724709369995; logfa
 # @group Textile
 #     tex = gram / kilometer = Tt
 #     dtex = decitex
-#     denier = gram / (9 * kilometer) = den = Td
+#     denier = gram / (9 * kilometer) = den
 #     jute = pound / (14400 * yard) = Tj
 #     aberdeen = jute = Ta
-#     RKM = kgf * 1000 / tex
+#     RKM  = gf / tex
 #
 #     number_english = 840 * yard / pound = Ne = NeC = ECC
 #     number_meter = kilometer / kilogram = Nm
diff --git a/gemd/units/impl.py b/gemd/units/impl.py
index 7622343..ee3f378 100644
--- a/gemd/units/impl.py
+++ b/gemd/units/impl.py
@@ -44,11 +44,6 @@ def _deploy_default_files() -> Tuple[Path, Path]:
 _ALLOWED_OPERATORS = {".", "+", "-", "*", "/", "//", "^", "**", "(", ")"}
 
 
-def _space_after_minus_preprocessor(input_string: str) -> str:
-    """A preprocessor that protects against a pint < 0.21 bug."""
-    return re.sub(r"(?<=-)\s+(?=\d)", "", input_string)
-
-
 def _scientific_notation_preprocessor(input_string: str) -> str:
     """Preprocessor that converts x * 10 ** y format to xEy."""
     def _as_scientific(matchobj: re.Match) -> str:
@@ -402,8 +397,7 @@ def change_definitions_file(filename: str = None):
         # Need to re-verify path because of some slippiness around tmp on macOS
         updated = (Path.cwd() / target.name).resolve(strict=True)
         _REGISTRY = _ScaleFactorRegistry(filename=updated,
-                                         preprocessors=[_space_after_minus_preprocessor,
-                                                        _scientific_notation_preprocessor,
+                                         preprocessors=[_scientific_notation_preprocessor,
                                                         _scaling_preprocessor
                                                         ],
                                          autoconvert_offset_to_baseunit=True
diff --git a/requirements.txt b/requirements.txt
index d97eb0e..29ad6a1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-pint==0.20
+pint==0.21
 deprecation==2.1.0
 typing-extensions==4.8.0
 importlib-resources==5.3.0
diff --git a/setup.py b/setup.py
index 6a10e4a..9602ea6 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@
           'tests.units': ['test_units.txt']
       },
       install_requires=[
-          "pint>=0.20,<0.24",
+          "pint>=0.21,<0.24",
           "deprecation>=2.1.0,<3",
           "typing_extensions>=4.8,<5",
           "importlib-resources>=5.3,<7"