diff --git a/lib/sord/type_converter.rb b/lib/sord/type_converter.rb
index 094d699..c79e38d 100644
--- a/lib/sord/type_converter.rb
+++ b/lib/sord/type_converter.rb
@@ -129,6 +129,8 @@ def self.yard_to_parlour(yard, item, config)
       case yard
       when nil # Type not specified
         Parlour::Types::Untyped.new
+      when "nil"
+        Parlour::Types::Raw.new('NilClass')
       when  "bool", "Bool", "boolean", "Boolean", "true", "false"
         Parlour::Types::Boolean.new
       when 'self'
@@ -195,10 +197,11 @@ def self.yard_to_parlour(yard, item, config)
         relative_generic_type = generic_type.start_with?('::') \
           ? generic_type[2..-1] : generic_type
 
-        parameters = split_type_parameters(type_parameters)
+        yard_parameters = split_type_parameters(type_parameters)
+        parameters = yard_parameters
           .map { |x| yard_to_parlour(x, item, config) }
-        if SINGLE_ARG_GENERIC_TYPES.include?(relative_generic_type) && parameters.length > 1
-          Parlour::Types.const_get(relative_generic_type).new(Parlour::Types::Union.new(parameters))
+        if SINGLE_ARG_GENERIC_TYPES.include?(relative_generic_type) && yard_parameters.length > 1
+          Parlour::Types.const_get(relative_generic_type).new(yard_to_parlour(yard_parameters, item, config))
         elsif relative_generic_type == 'Class'
           if parameters.length == 1
             Parlour::Types::Class.new(parameters.first)
diff --git a/spec/type_converter_spec.rb b/spec/type_converter_spec.rb
index 0a8f0b4..0a17533 100644
--- a/spec/type_converter_spec.rb
+++ b/spec/type_converter_spec.rb
@@ -77,6 +77,7 @@ def yard_to_parlour_default(type)
 
     context 'with literals' do
       it 'converts literals to their types' do
+        expect(yard_to_parlour_default('nil')).to eq Types::Raw.new('NilClass')
         expect(yard_to_parlour_default([':up', ':down'])).to eq Types::Raw.new('Symbol')
         expect(yard_to_parlour_default(['String', ':up', ':down'])).to eq \
           Types::Union.new(['String', 'Symbol'])
@@ -132,6 +133,11 @@ def self.path
           Types::Array.new(Types::Union.new(['String', 'Integer']))
       end
 
+      it 'handles nil is one of multiple arguments in a one-argument type parameter' do
+        expect(yard_to_parlour_default('Array<String, nil>')).to eq \
+          Types::Array.new(Types::Nilable.new('String'))
+      end
+
       it 'handles whitespace' do
         expect(yard_to_parlour_default('Array < String >')).to eq Types::Array.new('String')
       end
@@ -148,6 +154,7 @@ def self.path
       it 'handles correctly-formed two-argument type parameters with hash rockets' do
         expect(yard_to_parlour_default('Hash<String=>Symbol>')).to eq Types::Hash.new('String', 'Symbol')
         expect(yard_to_parlour_default('Hash{String=>Symbol}')).to eq Types::Hash.new('String', 'Symbol')
+        expect(yard_to_parlour_default('Hash{String=>String}')).to eq Types::Hash.new('String', 'String')
         expect(yard_to_parlour_default('Hash{String => Symbol}')).to eq Types::Hash.new('String', 'Symbol')
         expect(yard_to_parlour_default('Hash{String, Integer => Symbol, Float}')).to eq \
           Types::Hash.new(
@@ -339,7 +346,7 @@ def self.path
         Sord::TypeConverter::Configuration.new(
           output_language: :rbs,
           replace_errors_with_untyped: false,
-          replace_unresolved_with_untyped: false,  
+          replace_unresolved_with_untyped: false,
         )
       end