diff --git a/contrib/zk.lua b/contrib/zk.lua
index d2bfe435c7e7..b3054deac5fb 100644
--- a/contrib/zk.lua
+++ b/contrib/zk.lua
@@ -3,31 +3,40 @@ local l = require('lexer')
 local token, word_match = l.token, l.word_match
 local P, R, S = lpeg.P, lpeg.R, lpeg.S
 
-local M = {_NAME = 'zk'}
+local lex = l.new('zk', {fold_by_indentation = true})
 
 -- Whitespace.
-local ws = token(l.WHITESPACE, l.space^1)
+local indent = #l.starts_line(S(' \t')) *
+  (token(l.WHITESPACE, ' ') + token('indent_error', '\t'))^1
+lex:add_rule('indent', indent)
+lex:add_style('indent_error', {back = l.colors.red})
+lex:add_rule('whitespace', token(l.WHITESPACE, S(' \t')^1 + l.newline^1))
 
 -- Comments.
 local comment = token(l.COMMENT, '#' * l.nonnewline_esc^0)
+lex:add_rule('comment', comment)
 
 -- Strings.
 local dq_str = P('U')^-1 * l.range('"', true)
 local string = token(l.STRING, dq_str)
+lex:add_rule('string', string)
 
 -- Numbers.
 local number = token(l.NUMBER, l.integer)
+lex:add_rule('number', number)
 
 -- Keywords.
 local keyword = token(l.KEYWORD, word_match{
   'k', "field", 'constant', 'witness', 'circuit',
 })
+lex:add_rule('keyword', keyword)
 
 -- Constants.
 local constant = token(l.CONSTANT, word_match{
-	'true', 'false',
-	'VALUE_COMMIT_VALUE', 'VALUE_COMMIT_RANDOM', 'NULLIFIER_K',
+  'true', 'false',
+  'VALUE_COMMIT_VALUE', 'VALUE_COMMIT_RANDOM', 'NULLIFIER_K',
 })
+lex:add_rule('constant', constant)
 
 -- Types.
 local type = token(l.TYPE, word_match{
@@ -35,6 +44,7 @@ local type = token(l.TYPE, word_match{
   'EcNiPoint', 'Base', 'BaseArray', 'Scalar', 'ScalarArray',
   'MerklePath', 'Uint32', 'Uint64',
 })
+lex:add_rule('type', type)
 
 -- Instructions.
 local instruction = token('instruction', word_match{
@@ -47,24 +57,14 @@ local instruction = token('instruction', word_match{
   'constrain_equal_base', 'constrain_equal_point',
   'constrain_instance', 'debug',
 })
+lex:add_rule('instruction', instruction)
 
 -- Identifiers.
 local identifier = token(l.IDENTIFIER, l.word)
+lex:add_rule('identifier', identifier)
 
 -- Operators.
 local operator = token(l.OPERATOR, S('(){}=;,'))
+lex:add_rule('operator', operator)
 
-M._rules = {
-  {'whitespace', ws},
-  {'comment', comment},
-  {'keyword', keyword},
-  {'type', type},
-  {'constant', constant},
-  {'string', string},
-  {'number', number},
-  {'instruction', instruction},
-  {'identifier', identifier},
-  {'operator', operator},
-}
-
-return M
+return lex