diff --git a/lexer.l b/lexer.l
index e604adab..fe0049a9 100644
--- a/lexer.l
+++ b/lexer.l
@@ -107,7 +107,7 @@
 }
   
 
-[[:alnum:]]+  { yylval->literal = jv_string(yytext); return IDENT;}
+[a-zA-Z_][a-zA-Z_0-9]*  { yylval->literal = jv_string(yytext); return IDENT;}
 
 [ \n\t]+  {}
 
diff --git a/testdata b/testdata
index 8a289973..307eaa62 100644
--- a/testdata
+++ b/testdata
@@ -61,6 +61,10 @@ null
 {"foo": {"bar": 42}, "bar": "badvalue"}
 42
 
+.foo_bar
+{"foo_bar": 2}
+2
+
 .["foo"].bar
 {"foo": {"bar": 42}, "bar": "badvalue"}
 42