diff --git a/substrate/primitives/authorship/src/lib.rs b/substrate/primitives/authorship/src/lib.rs
index 254078b844..ac4b5fd315 100644
--- a/substrate/primitives/authorship/src/lib.rs
+++ b/substrate/primitives/authorship/src/lib.rs
@@ -21,7 +21,9 @@
 
 use sp_std::{prelude::*, result::Result};
 
-use codec::{Decode, Encode};
+#[cfg(feature = "std")]
+use codec::Decode;
+use codec::Encode;
 use sp_inherents::{Error, InherentData, InherentIdentifier, IsFatalError};
 use sp_runtime::{traits::Header as HeaderT, RuntimeString};
 
diff --git a/substrate/primitives/npos-elections/src/assignments.rs b/substrate/primitives/npos-elections/src/assignments.rs
index b0dd29dc19..da101e64a7 100644
--- a/substrate/primitives/npos-elections/src/assignments.rs
+++ b/substrate/primitives/npos-elections/src/assignments.rs
@@ -18,6 +18,7 @@
 //! Structs and helpers for distributing a voter's stake among various winners.
 
 use crate::{Error, ExtendedBalance, IdentifierT, PerThing128, __OrInvalidIndex};
+#[cfg(feature = "std")]
 use codec::{Decode, Encode};
 use sp_arithmetic::{
 	traits::{Bounded, Zero},
diff --git a/substrate/utils/prometheus/src/lib.rs b/substrate/utils/prometheus/src/lib.rs
index 96407b0062..3753ab9061 100644
--- a/substrate/utils/prometheus/src/lib.rs
+++ b/substrate/utils/prometheus/src/lib.rs
@@ -15,7 +15,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#[cfg(not(target_os = "unknown"))]
 use futures_util::{future::Future, FutureExt};
+use prometheus::core::Collector;
 pub use prometheus::{
 	self,
 	core::{
@@ -25,7 +27,8 @@ pub use prometheus::{
 	exponential_buckets, Error as PrometheusError, Histogram, HistogramOpts, HistogramVec, Opts,
 	Registry,
 };
-use prometheus::{core::Collector, Encoder, TextEncoder};
+#[cfg(not(target_os = "unknown"))]
+use prometheus::{Encoder, TextEncoder};
 use std::net::SocketAddr;
 
 #[cfg(not(target_os = "unknown"))]