diff --git a/lib/oga/css/lexer.rl b/lib/oga/css/lexer.rl
index db04853..0ae936c 100644
--- a/lib/oga/css/lexer.rl
+++ b/lib/oga/css/lexer.rl
@@ -155,7 +155,7 @@ module Oga
         # Identifiers are used for element and attribute names. Identifiers have
         # to start with a letter.
 
-        identifier = '*' | [a-zA-Z]+ [a-zA-Z\-_0-9]*;
+        identifier = '*' | [a-zA-Z_]+ [a-zA-Z\-_0-9]*;
 
         action emit_identifier {
           emit(:T_IDENT, ts, te)
diff --git a/spec/oga/css/lexer/paths_spec.rb b/spec/oga/css/lexer/paths_spec.rb
index 8bcd30d..9bc3183 100644
--- a/spec/oga/css/lexer/paths_spec.rb
+++ b/spec/oga/css/lexer/paths_spec.rb
@@ -6,6 +6,10 @@ describe Oga::CSS::Lexer do
       lex_css('h3').should == [[:T_IDENT, 'h3']]
     end
 
+    example 'lex a simple path starting with an underscore' do
+      lex_css('_h3').should == [[:T_IDENT, '_h3']]
+    end
+
     example 'lex a path with two members' do
       lex_css('div h3').should == [
         [:T_IDENT, 'div'],