diff --git a/northstar-runtime/src/common/version.rs b/northstar-runtime/src/common/version.rs
index b7c1ac5eb..ca9f01c84 100644
--- a/northstar-runtime/src/common/version.rs
+++ b/northstar-runtime/src/common/version.rs
@@ -1,5 +1,9 @@
 use serde::{Deserialize, Serialize};
-use std::{cmp::Ordering, fmt, str::FromStr};
+use std::{
+    cmp::Ordering,
+    fmt::{self, Display},
+    str::FromStr,
+};
 use thiserror::Error;
 
 /// Parsing error
@@ -164,9 +168,9 @@ impl FromStr for VersionReq {
     }
 }
 
-impl ToString for VersionReq {
-    fn to_string(&self) -> String {
-        self.inner.to_string()
+impl Display for VersionReq {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.inner)
     }
 }
 
diff --git a/northstar-runtime/src/npk/manifest/mod.rs b/northstar-runtime/src/npk/manifest/mod.rs
index 7dc9f30e5..93effb736 100644
--- a/northstar-runtime/src/npk/manifest/mod.rs
+++ b/northstar-runtime/src/npk/manifest/mod.rs
@@ -198,16 +198,6 @@ impl FromStr for Manifest {
     }
 }
 
-impl ToString for Manifest {
-    #[allow(clippy::unwrap_used)]
-    fn to_string(&self) -> String {
-        // A `Manifest` is convertible to `String` as long as its implementation of `Serialize` does
-        // not return an error. This should never happen for the types that we use in `Manifest` so
-        // we can safely use .unwrap() here.
-        serde_yaml::to_string(self).expect("failed to serialize manifest")
-    }
-}
-
 /// Validate manifest.
 fn validate(manifest: &Manifest) -> Result<(), ValidationError> {
     // Most optionals in the manifest are not valid for a resource container
diff --git a/northstar-runtime/src/npk/npk.rs b/northstar-runtime/src/npk/npk.rs
index 8e12cd886..477c9caab 100644
--- a/northstar-runtime/src/npk/npk.rs
+++ b/northstar-runtime/src/npk/npk.rs
@@ -499,7 +499,8 @@ impl<'a> NpkBuilder<'a> {
         zip.set_comment(meta_str);
 
         // Add manifest.
-        let manifest_str = manifest.to_string();
+        let manifest_str =
+            serde_yaml::to_string(manifest).context("failed to serialize manifest")?;
         zip.start_file(MANIFEST_NAME, options)
             .context("failed to write manifest to NPK")?;
         zip.write_all(manifest_str.as_bytes())
diff --git a/northstar-runtime/src/runtime/ipc/raw_fd_ext.rs b/northstar-runtime/src/runtime/ipc/raw_fd_ext.rs
index e3b5ab2e4..a30a345ea 100644
--- a/northstar-runtime/src/runtime/ipc/raw_fd_ext.rs
+++ b/northstar-runtime/src/runtime/ipc/raw_fd_ext.rs
@@ -3,6 +3,7 @@ use std::{io, io::Result, os::unix::prelude::AsRawFd};
 
 pub trait RawFdExt: AsRawFd {
     /// Returns true of self is set to non-blocking.
+    #[allow(unused)]
     fn is_nonblocking(&self) -> Result<bool>;
 
     /// Set non-blocking mode.
diff --git a/northstar-runtime/src/runtime/mod.rs b/northstar-runtime/src/runtime/mod.rs
index a67847b50..e16bda410 100644
--- a/northstar-runtime/src/runtime/mod.rs
+++ b/northstar-runtime/src/runtime/mod.rs
@@ -1,6 +1,7 @@
 mod cgroups;
 mod console;
 mod debug;
+#[allow(unused)]
 mod devicemapper;
 mod env;
 mod error;