diff --git a/src/datetime.rs b/src/datetime.rs
index 7e32da7..92cf178 100644
--- a/src/datetime.rs
+++ b/src/datetime.rs
@@ -1141,7 +1141,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_nanoseconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};
@@ -1432,7 +1432,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_milliseconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};
@@ -1719,7 +1719,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_seconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};
diff --git a/src/naive/date.rs b/src/naive/date.rs
index 9ac240f..f0e63e2 100644
--- a/src/naive/date.rs
+++ b/src/naive/date.rs
@@ -3,6 +3,7 @@
 
 //! ISO 8601 calendar date without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt};
 use core::ops::{Add, Sub, AddAssign, SubAssign};
diff --git a/src/naive/datetime.rs b/src/naive/datetime.rs
index ba9cf4f..50ba8b0 100644
--- a/src/naive/datetime.rs
+++ b/src/naive/datetime.rs
@@ -3,6 +3,7 @@
 
 //! ISO 8601 date and time without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt, hash};
 use core::ops::{Add, Sub, AddAssign, SubAssign};
diff --git a/src/naive/time.rs b/src/naive/time.rs
index ff02f4d..4ce520c 100644
--- a/src/naive/time.rs
+++ b/src/naive/time.rs
@@ -3,6 +3,7 @@
 
 //! ISO 8601 time without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt, hash};
 use core::ops::{Add, Sub, AddAssign, SubAssign};