diff --git a/lib/oga/css/parser.y b/lib/oga/css/parser.y
index c83bc09..73b36fe 100644
--- a/lib/oga/css/parser.y
+++ b/lib/oga/css/parser.y
@@ -122,14 +122,25 @@ rule
     ;
 
   pseudo_class
+    # :root
+    : pseudo_name { s(:pseudo, val[0]) }
+
     # x:root
-    : path_member T_COLON T_IDENT { s(:pseudo, val[2], val[0]) }
+    | path_member pseudo_name { s(:pseudo, val[1], val[0]) }
+
+    # :nth-child(2)
+    | pseudo_name pseudo_args { s(:pseudo, val[0], nil, val[1]) }
 
     # x:nth-child(2)
-    | path_member T_COLON T_IDENT T_LPAREN pseudo_arg T_RPAREN
-      {
-        s(:pseudo, val[2], val[0], val[4])
-      }
+    | path_member pseudo_name pseudo_args { s(:pseudo, val[1], val[0], val[2]) }
+    ;
+
+  pseudo_name
+    : T_COLON T_IDENT { val[1] }
+    ;
+
+  pseudo_args
+    : T_LPAREN pseudo_arg T_RPAREN { val[1] }
     ;
 
   pseudo_arg
diff --git a/spec/oga/css/parser/pseudo_classes_spec.rb b/spec/oga/css/parser/pseudo_classes_spec.rb
index de90e4c..0466b0b 100644
--- a/spec/oga/css/parser/pseudo_classes_spec.rb
+++ b/spec/oga/css/parser/pseudo_classes_spec.rb
@@ -2,11 +2,15 @@ require 'spec_helper'
 
 describe Oga::CSS::Parser do
   context 'pseudo classes' do
-    example 'parse the :root pseudo class' do
+    example 'parse the x:root pseudo class' do
       parse_css('x:root').should == s(:pseudo, 'root', s(:test, nil, 'x'))
     end
 
-    example 'parse the x:nth-child pseudo class' do
+    example 'parse the :root pseudo class' do
+      parse_css(':root').should == s(:pseudo, 'root')
+    end
+
+    example 'parse the x:nth-child(1) pseudo class' do
       parse_css('x:nth-child(1)').should == s(
         :pseudo,
         'nth-child',
@@ -15,6 +19,15 @@ describe Oga::CSS::Parser do
       )
     end
 
+    example 'parse the :nth-child(1) pseudo class' do
+      parse_css(':nth-child(1)').should == s(
+        :pseudo,
+        'nth-child',
+        nil,
+        s(:int, 1)
+      )
+    end
+
     example 'parse the x:nth-child(odd) pseudo class' do
       parse_css('x:nth-child(odd)').should == s(
         :pseudo,