diff --git a/vlib/v/util/util.v b/vlib/v/util/util.v
index 354a6f75e1..305532b8e6 100644
--- a/vlib/v/util/util.v
+++ b/vlib/v/util/util.v
@@ -129,7 +129,7 @@ pub fn launch_tool(is_verbose bool, tool_name string, args []string) {
 	mut tool_source := ''
 	if os.is_dir(tool_basename) {
 		tool_exe = path_of_executable(os.join_path(tool_basename, tool_name))
-		tool_source = os.join_path(tool_basename, tool_name + '.v')
+		tool_source = tool_basename
 	} else {
 		tool_exe = path_of_executable(tool_basename)
 		tool_source = tool_basename + '.v'
@@ -139,9 +139,10 @@ pub fn launch_tool(is_verbose bool, tool_name string, args []string) {
 		println('launch_tool vexe        : $vroot')
 		println('launch_tool vroot       : $vroot')
 		println('launch_tool tool_args   : $tool_args')
+		println('launch_tool tool_source : $tool_source')
 		println('launch_tool tool_command: $tool_command')
 	}
-	should_compile := should_recompile_tool(vexe, tool_source)
+	should_compile := should_recompile_tool(vexe, tool_source, tool_name, tool_exe)
 	if is_verbose {
 		println('launch_tool should_compile: $should_compile')
 	}
@@ -167,13 +168,26 @@ pub fn launch_tool(is_verbose bool, tool_name string, args []string) {
 	exit(os.system(tool_command))
 }
 
-// NB: should_recompile_tool/2 compares unix timestamps that have 1 second resolution
+// NB: should_recompile_tool/4 compares unix timestamps that have 1 second resolution
 // That means that a tool can get recompiled twice, if called in short succession.
 // TODO: use a nanosecond mtime timestamp, if available.
-pub fn should_recompile_tool(vexe string, tool_source string) bool {
-	sfolder := os.dir(tool_source)
-	tool_name := os.base(tool_source).replace('.v', '')
-	tool_exe := os.join_path(sfolder, path_of_executable(tool_name))
+pub fn should_recompile_tool(vexe string, tool_source string, tool_name string, tool_exe string) bool {
+	if os.is_dir(tool_source) {
+		source_files := os.walk_ext(tool_source, '.v')
+		mut newest_sfile := ''
+		mut newest_sfile_mtime := 0
+		for sfile in source_files {
+			mtime := os.file_last_mod_unix(sfile)
+			if mtime > newest_sfile_mtime {
+				newest_sfile_mtime = mtime
+				newest_sfile = sfile
+			}
+		}
+		single_file_recompile := should_recompile_tool(vexe, newest_sfile, tool_name,
+			tool_exe)
+		// eprintln('>>> should_recompile_tool: tool_source: $tool_source | $single_file_recompile | $newest_sfile')
+		return single_file_recompile
+	}
 	// TODO Caching should be done on the `vlib/v` level.
 	mut should_compile := false
 	if !os.exists(tool_exe) {
@@ -212,6 +226,13 @@ pub fn should_recompile_tool(vexe string, tool_source string) bool {
 	return should_compile
 }
 
+fn tool_source2name_and_exe(tool_source string) (string, string) {
+	sfolder := os.dir(tool_source)
+	tool_name := os.base(tool_source).replace('.v', '')
+	tool_exe := os.join_path(sfolder, path_of_executable(tool_name))
+	return tool_name, tool_exe
+}
+
 pub fn quote_path(s string) string {
 	mut qs := s
 	if qs.contains('&') {
@@ -424,7 +445,8 @@ pub fn prepare_tool_when_needed(source_name string) {
 	vexe := os.getenv('VEXE')
 	vroot := os.dir(vexe)
 	stool := os.join_path(vroot, 'cmd', 'tools', source_name)
-	if should_recompile_tool(vexe, stool) {
+	tool_name, tool_exe := tool_source2name_and_exe(stool)
+	if should_recompile_tool(vexe, stool, tool_name, tool_exe) {
 		time.sleep_ms(1001) // TODO: remove this when we can get mtime with a better resolution
 		recompile_file(vexe, stool)
 	}