diff --git a/language/pl0/pl0.cc b/language/pl0/pl0.cc
index 89b7e61..8ce8896 100644
--- a/language/pl0/pl0.cc
+++ b/language/pl0/pl0.cc
@@ -20,21 +20,21 @@ auto grammar = R"(
     program    <- _ block '.' _
 
     block      <- const var procedure statement
-    const      <- ('CONST' _ ident '=' _ number (',' _ ident '=' _ number)* ';' _)?
-    var        <- ('VAR' _ ident (',' _ ident)* ';' _)?
-    procedure  <- ('PROCEDURE' _ ident ';' _ block ';' _)*
+    const      <- ('CONST' __ ident '=' _ number (',' _ ident '=' _ number)* ';' _)?
+    var        <- ('VAR' __ ident (',' _ ident)* ';' _)?
+    procedure  <- ('PROCEDURE' __ ident ';' _ block ';' _)*
 
     statement  <- (assignment / call / statements / if / while / out / in)?
     assignment <- ident ':=' _ expression
-    call       <- 'CALL' _ ident
-    statements <- 'BEGIN' _ statement (';' _ statement )* 'END' _
-    if         <- 'IF' _ condition 'THEN' _ statement
-    while      <- 'WHILE' _ condition 'DO' _ statement
-    out        <- ('out' / 'write' / '!') _ expression
-    in         <- ('in' / 'read' / '?') _ ident
+    call       <- 'CALL' __ ident
+    statements <- 'BEGIN' __ statement (';' _ statement )* 'END' __
+    if         <- 'IF' __ condition 'THEN' __ statement
+    while      <- 'WHILE' __ condition 'DO' __ statement
+    out        <- ('out' __ / 'write' __ / '!' _) expression
+    in         <- ('in' __ / 'read' __ / '?' _) ident
 
     condition  <- odd / compare
-    odd        <- 'ODD' _ expression
+    odd        <- 'ODD' __ expression
     compare    <- expression compare_op expression
     compare_op <- < '=' / '#' / '<=' / '<' / '>=' / '>' > _
 
@@ -47,10 +47,11 @@ auto grammar = R"(
 
     factor     <- ident / number / '(' _ expression ')' _
 
-    ident      <- < [a-z] ([a-z] / [0-9])* > _
+    ident      <- < [a-z] [a-z0-9]* > _
     number     <- < [0-9]+ > _
 
     ~_         <- [ \t\r\n]*
+    ~__        <- ![a-z0-9_] _
 )";
 
 /*