diff --git a/cmd/tools/oldv.v b/cmd/tools/oldv.v
index 03eaf83ef5..08b3083e91 100644
--- a/cmd/tools/oldv.v
+++ b/cmd/tools/oldv.v
@@ -123,7 +123,7 @@ fn main() {
 	}
 	should_sync := fp.bool('cache-sync', `s`, false, 'Update the local cache')
 	if !should_sync {
-		fp.limit_free_args(1, 1)
+		fp.limit_free_args(1, 1) ?
 	}
 	////
 	context.cleanup = fp.bool('clean', 0, false, 'Clean before running (slower).')
diff --git a/cmd/tools/performance_compare.v b/cmd/tools/performance_compare.v
index 6723231524..648defd907 100644
--- a/cmd/tools/performance_compare.v
+++ b/cmd/tools/performance_compare.v
@@ -192,7 +192,7 @@ fn main() {
 	fp.description(tool_description)
 	fp.arguments_description('COMMIT_BEFORE [COMMIT_AFTER]')
 	fp.skip_executable()
-	fp.limit_free_args(1, 2)
+	fp.limit_free_args(1, 2) ?
 	context.vflags = fp.string('vflags', 0, '', 'Additional options to pass to the v commands, for example "-cc tcc"')
 	context.hyperfineopts = fp.string('hyperfine_options', 0, '', 'Additional options passed to hyperfine.
 ${flag.space}For example on linux, you may want to pass:
diff --git a/cmd/tools/repeat.v b/cmd/tools/repeat.v
index e69cfdfde7..8adc565d92 100644
--- a/cmd/tools/repeat.v
+++ b/cmd/tools/repeat.v
@@ -143,19 +143,19 @@ const (
 
 fn main() {
 	mut context := Context{}
-	context.parse_options()
+	context.parse_options() ?
 	context.run()
 	context.show_diff_summary()
 }
 
-fn (mut context Context) parse_options() {
+fn (mut context Context) parse_options() ? {
 	mut fp := flag.new_flag_parser(os.args)
 	fp.application(os.file_name(os.executable()))
 	fp.version('0.0.1')
 	fp.description('Repeat command(s) and collect statistics. NB: you have to quote each command, if it contains spaces.')
 	fp.arguments_description('CMD1 CMD2 ...')
 	fp.skip_executable()
-	fp.limit_free_args_to_at_least(1)
+	fp.limit_free_args_to_at_least(1) ?
 	context.count = fp.int('count', `c`, 10, 'Repetition count.')
 	context.series = fp.int('series', `s`, 2, 'Series count. `-s 2 -c 4 a b` => aaaabbbbaaaabbbb, while `-s 3 -c 2 a b` => aabbaabbaabb.')
 	context.warmup = fp.int('warmup', `w`, 2, 'Warmup runs. These are done *only at the start*, and are ignored.')
diff --git a/cmd/tools/vast/vast.v b/cmd/tools/vast/vast.v
index 8a6c008dd2..b037d1f6b7 100644
--- a/cmd/tools/vast/vast.v
+++ b/cmd/tools/vast/vast.v
@@ -46,7 +46,7 @@ fn main() {
 	for hf in hfields.split(',') {
 		mhf.names[hf] = true
 	}
-	fp.limit_free_args_to_at_least(1)
+	fp.limit_free_args_to_at_least(1) ?
 	rest_of_args := fp.remaining_parameters()
 	for vfile in rest_of_args {
 		file := get_abs_path(vfile)
diff --git a/cmd/tools/vwatch.v b/cmd/tools/vwatch.v
index 0ac243d7ab..e718ea5a51 100644
--- a/cmd/tools/vwatch.v
+++ b/cmd/tools/vwatch.v
@@ -314,7 +314,7 @@ fn main() {
 	fp.description('Collect all .v files needed for a compilation, then re-run the compilation when any of the source changes.')
 	fp.arguments_description('[--silent] [--clear] [--ignore .db] [--add /path/to/a/file.v] [run] program.v')
 	fp.allow_unknown_args()
-	fp.limit_free_args_to_at_least(1)
+	fp.limit_free_args_to_at_least(1) ?
 	context.is_worker = fp.bool('vwatchworker', 0, false, 'Internal flag. Used to distinguish vwatch manager and worker processes.')
 	context.silent = fp.bool('silent', `s`, false, 'Be more silent; do not print the watch timestamp before each re-run.')
 	context.clear_terminal = fp.bool('clear', `c`, false, 'Clears the terminal before each re-run.')
diff --git a/vlib/flag/README.md b/vlib/flag/README.md
index 1122f77f55..87c94e604e 100644
--- a/vlib/flag/README.md
+++ b/vlib/flag/README.md
@@ -17,7 +17,7 @@ fn main() {
 	mut fp := flag.new_flag_parser(os.args)
 	fp.application('flag_example_tool')
 	fp.version('v0.0.1')
-	fp.limit_free_args(0, 0) // comment this, if you expect arbitrary texts after the options
+	fp.limit_free_args(0, 0) ? // comment this, if you expect arbitrary texts after the options
 	fp.description('This tool is only designed to show how the flag lib is working')
 	fp.skip_executable()
 	an_int := fp.int('an_int', 0, 0o123, 'some int to define 0o123 is its default value')
diff --git a/vlib/flag/flag.v b/vlib/flag/flag.v
index 85bb09de7f..21f4731d87 100644
--- a/vlib/flag/flag.v
+++ b/vlib/flag/flag.v
@@ -429,22 +429,22 @@ pub fn (mut fs FlagParser) string(name string, abbr byte, sdefault string, usage
 	return value
 }
 
-pub fn (mut fs FlagParser) limit_free_args_to_at_least(n int) {
+pub fn (mut fs FlagParser) limit_free_args_to_at_least(n int) ? {
 	if n > flag.max_args_number {
-		panic('flag.limit_free_args_to_at_least expect n to be smaller than $flag.max_args_number')
+		return error('flag.limit_free_args_to_at_least expect n to be smaller than $flag.max_args_number')
 	}
 	if n <= 0 {
-		panic('flag.limit_free_args_to_at_least expect n to be a positive number')
+		return error('flag.limit_free_args_to_at_least expect n to be a positive number')
 	}
 	fs.min_free_args = n
 }
 
-pub fn (mut fs FlagParser) limit_free_args_to_exactly(n int) {
+pub fn (mut fs FlagParser) limit_free_args_to_exactly(n int) ? {
 	if n > flag.max_args_number {
-		panic('flag.limit_free_args_to_exactly expect n to be smaller than $flag.max_args_number')
+		return error('flag.limit_free_args_to_exactly expect n to be smaller than $flag.max_args_number')
 	}
 	if n < 0 {
-		panic('flag.limit_free_args_to_exactly expect n to be a non negative number')
+		return error('flag.limit_free_args_to_exactly expect n to be a non negative number')
 	}
 	fs.min_free_args = n
 	fs.max_free_args = n
@@ -452,9 +452,9 @@ pub fn (mut fs FlagParser) limit_free_args_to_exactly(n int) {
 
 // this will cause an error in finalize() if free args are out of range
 // (min, ..., max)
-pub fn (mut fs FlagParser) limit_free_args(min int, max int) {
+pub fn (mut fs FlagParser) limit_free_args(min int, max int) ? {
 	if min > max {
-		panic('flag.limit_free_args expect min < max, got $min >= $max')
+		return error('flag.limit_free_args expect min < max, got $min >= $max')
 	}
 	fs.min_free_args = min
 	fs.max_free_args = max
diff --git a/vlib/flag/flag_test.v b/vlib/flag/flag_test.v
index 83261932b2..be52e9788b 100644
--- a/vlib/flag/flag_test.v
+++ b/vlib/flag/flag_test.v
@@ -153,9 +153,9 @@ fn test_finalize_returns_error_for_unknown_flags_short() {
 	assert finalized.len < 0 // expect error to be returned
 }
 
-fn test_allow_to_build_usage_message() {
+fn test_allow_to_build_usage_message() ? {
 	mut fp := flag.new_flag_parser([])
-	fp.limit_free_args(1, 4)
+	fp.limit_free_args(1, 4) ?
 	fp.application('flag_tool')
 	fp.version('v0.0.0')
 	fp.description('some short information about this tool')
@@ -194,9 +194,9 @@ fn test_if_no_options_given_usage_message_does_not_contain_options() {
 	assert !fp.usage().contains('Options:')
 }
 
-fn test_free_args_could_be_limited() {
+fn test_free_args_could_be_limited() ? {
 	mut fp1 := flag.new_flag_parser(['a', 'b', 'c'])
-	fp1.limit_free_args(1, 4)
+	fp1.limit_free_args(1, 4) ?
 	args := fp1.finalize() or {
 		assert false
 		return
@@ -206,9 +206,9 @@ fn test_free_args_could_be_limited() {
 	assert args[2] == 'c'
 }
 
-fn test_error_for_to_few_free_args() {
+fn test_error_for_to_few_free_args() ? {
 	mut fp1 := flag.new_flag_parser(['a', 'b', 'c'])
-	fp1.limit_free_args(5, 6)
+	fp1.limit_free_args(5, 6) ?
 	args := fp1.finalize() or {
 		assert err.msg.starts_with('Expected at least 5 arguments')
 		return
@@ -216,9 +216,9 @@ fn test_error_for_to_few_free_args() {
 	assert args.len < 0 // expect an error and need to use args
 }
 
-fn test_error_for_to_much_free_args() {
+fn test_error_for_to_much_free_args() ? {
 	mut fp1 := flag.new_flag_parser(['a', 'b', 'c'])
-	fp1.limit_free_args(1, 2)
+	fp1.limit_free_args(1, 2) ?
 	args := fp1.finalize() or {
 		assert err.msg.starts_with('Expected at most 2 arguments')
 		return
@@ -226,9 +226,9 @@ fn test_error_for_to_much_free_args() {
 	assert args.len < 0 // expect an error and need to use args
 }
 
-fn test_could_expect_no_free_args() {
+fn test_could_expect_no_free_args() ? {
 	mut fp1 := flag.new_flag_parser(['a'])
-	fp1.limit_free_args(0, 0)
+	fp1.limit_free_args(0, 0) ?
 	args := fp1.finalize() or {
 		assert err.msg.starts_with('Expected no arguments')
 		return