diff --git a/src/os/exec/lp_plan9.go b/src/os/exec/lp_plan9.go
index 0430af9eef..f713a6905c 100644
--- a/src/os/exec/lp_plan9.go
+++ b/src/os/exec/lp_plan9.go
@@ -36,7 +36,7 @@ func findExecutable(file string) error {
 // As of Go 1.19, LookPath will instead return that path along with an error satisfying
 // [errors.Is](err, [ErrDot]). See the package documentation for more details.
 func LookPath(file string) (string, error) {
-	if err := validateLookPath(file); err != nil {
+	if err := validateLookPath(filepath.Clean(file)); err != nil {
 		return "", &Error{file, err}
 	}