diff --git a/vlib/flag/flag.v b/vlib/flag/flag.v
index cd9f3e5c61..99ebdd1791 100644
--- a/vlib/flag/flag.v
+++ b/vlib/flag/flag.v
@@ -23,7 +23,7 @@ module flag
 //
 //  	fp.skip_executable()
 //
-//  	an_int := fp.int('an_int', 666, 'some int to define 666 is default')
+//  	an_int := fp.int('an_int', 0o666, 'some int to define 0o666 is default')
 //  	a_bool := fp.bool('a_bool', false, 'some \'real\' flag')
 //  	a_float := fp.float('a_float', 1.0, 'also floats')
 //  	a_string := fp.string('a_string', 'no text', 'finally, some text')
diff --git a/vlib/flag/flag_test.v b/vlib/flag/flag_test.v
index 5851434779..aede4b761d 100644
--- a/vlib/flag/flag_test.v
+++ b/vlib/flag/flag_test.v
@@ -35,7 +35,7 @@ fn test_flags_could_be_defined_with_eq() {
 	'--a_string=stuff',
 	'--a_bool=true'])
 
-	assert 42 == fp.int('an_int', 0, 666, '')
+	assert 42 == fp.int('an_int', 0, 0o666, '')
 	&& true == fp.bool('a_bool', 0, false, '')
 	&& true == fp.bool('bool_without', 0, false, '')
 	&& 2.0 == fp.float('a_float', 0, 1.0, '')
@@ -50,7 +50,7 @@ fn test_values_could_be_defined_without_eq() {
 	'--a_string', 'stuff',
 	'--a_bool', 'true'])
 
-	assert 42 == fp.int('an_int', 0, 666, '')
+	assert 42 == fp.int('an_int', 0, 0o666, '')
 	&& true == fp.bool('a_bool', 0, false, '')
 	&& true == fp.bool('bool_without', 0, false, '')
 	&& 2.0 == fp.float('a_float', 0, 1.0, '')
@@ -65,7 +65,7 @@ fn test_values_could_be_defined_mixed() {
 	'--a_string', 'stuff',
 	'--a_bool=true'])
 
-	assert 42 == fp.int('an_int', 0, 666, '')
+	assert 42 == fp.int('an_int', 0, 0o666, '')
 	&& true == fp.bool('a_bool', 0, false, '')
 	&& true == fp.bool('bool_without', 0, false, '')
 	&& 2.0 == fp.float('a_float', 0, 1.0, '')
@@ -78,8 +78,8 @@ fn test_beaware_for_argument_names_with_same_prefix() {
 	'--shorter=7'
 	])
 
-	assert 5 == fp.int('short', 0, 666, '')
-	&& 7 == fp.int('shorter', 0, 666, '')
+	assert 5 == fp.int('short', 0, 0o666, '')
+	&& 7 == fp.int('shorter', 0, 0o666, '')
 }
 
 fn test_beaware_for_argument_names_with_same_prefix_inverse() {
@@ -88,8 +88,8 @@ fn test_beaware_for_argument_names_with_same_prefix_inverse() {
 	'--short', '5',
 	])
 
-	assert 5 == fp.int('short', 0, 666, '')
-	&& 7 == fp.int('shorter', 0, 666, '')
+	assert 5 == fp.int('short', 0, 0o666, '')
+	&& 7 == fp.int('shorter', 0, 0o666, '')
 }
 
 fn test_allow_to_skip_executable_path() {
@@ -108,7 +108,7 @@ fn test_none_flag_arguments_are_allowed() {
 	mut fp := flag.new_flag_parser([
 	'file1', '--an_int=2', 'file2', 'file3', '--bool_without', 'file4', '--outfile', 'outfile'])
 
-	assert 2 == fp.int('an_int', 0, 666, '')
+	assert 2 == fp.int('an_int', 0, 0o666, '')
 	&& 'outfile' == fp.string('outfile', 0, 'bad', '')
 	&& true == fp.bool('bool_without', 0, false, '')
 }
@@ -149,7 +149,7 @@ fn test_allow_to_build_usage_message() {
 	fp.version('v0.0.0')
 	fp.description('some short information about this tool')
 
-	fp.int('an_int', 0, 666, 'some int to define')
+	fp.int('an_int', 0, 0o666, 'some int to define')
 	fp.bool('a_bool', 0, false, 'some bool to define')
 	fp.bool('bool_without_but_really_big', 0, false, 'this should appear on the next line')
 	fp.float('a_float', 0, 1.0, 'some float as well')