diff --git a/Cargo.toml b/Cargo.toml
index 7f6694a..645fc42 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -29,7 +29,7 @@ readme = "README.md"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-tokio = {version = "1.17.0", features = ["io-util", "time"] }
+tokio = {version = "1.17.0", features = ["io-util", "time", "fs"] }
 tokio-serial = "5.4.1"
 futures = "0.3.21"
 cobs = "0.2"
diff --git a/src/lib.rs b/src/lib.rs
index dd11ff6..5819c91 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -427,14 +427,14 @@ impl ZSerial {
 
     async fn check_device(&self) -> tokio_serial::Result<()> {
         // check if the file is still there
-        if !tokio::fs::metadata(self.port.clone()).await.is_ok() {
+        if tokio::fs::metadata(self.port.clone()).await.is_err() {
             // the file does not exist anymore returing an error
             return Err(tokio_serial::Error::new(
                 tokio_serial::ErrorKind::NoDevice,
-                format!("Serial device disappeared"),
+                "Serial device disappeared".to_string(),
             ));
         }
-        return Ok(());
+        Ok(())
     }
     async fn internal_read(&mut self, buff: &mut [u8]) -> tokio_serial::Result<(usize, Header)> {
         //check if the device is sitll there