*vc-diff*.diff

diff --git a/lib/ruby_units.rb b/lib/ruby_units.rb
index 4aaf462..cd51437 100644
--- a/lib/ruby_units.rb
+++ b/lib/ruby_units.rb
@@ -141,6 +141,8 @@ class Unit
         actual_numerator, actual_denominator = actual
         new_numerator += actual_numerator
         new_denominator += actual_denominator
+      elsif :unitless == Unit.definition(unit_part).kind
+        # ignore unitless, e.g. "%"
       else
         new_numerator << unit_part
       end
@@ -151,6 +153,8 @@ class Unit
         actual_numerator, actual_denominator = actual
         new_numerator += actual_denominator
         new_denominator += actual_numerator
+      elsif :unitless == Unit.definition(unit_part).kind
+        # ignore unitless, e.g. "%"
       else
         new_denominator << unit_part
       end

test

diff --git a/spec/lib/ruby_units_spec.rb b/spec/lib/ruby_units_spec.rb
index 5096ba0..cc0f558 100644
--- a/spec/lib/ruby_units_spec.rb
+++ b/spec/lib/ruby_units_spec.rb
@@ -121,6 +121,11 @@ describe Unit do
       Unit.new("70000 kg*l^2/100l^2*ha").reduce_units.should == Unit.new("7 kg/ha")
     end
 
+    context 'reduces percentages' do
+      out = (Unit.new("5 %") * Unit.new("100 kg")).reduce_units
+      out.should == Unit.new("5 kg")
+    end
+
     context 'handle SI prefixes properly' do
       # why is left side converted to float? is it because we are not using Rational?
       Unit.new("1 lb*kl/l").reduce_units.units == Unit.new("1000 lb").units