diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index da9afdd2ca37b..663e1ac915dbf 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -378,6 +378,7 @@ impl String {
     /// ```
     /// let s = String::new();
     /// ```
+    #[must_use = "newly created String must be used"]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_string_new")]
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 690cbcb559bbf..312aad361041e 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -320,6 +320,7 @@ impl<T> Vec<T> {
     /// # #![allow(unused_mut)]
     /// let mut vec: Vec<i32> = Vec::new();
     /// ```
+    #[must_use = "newly created vector must be used"]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_unstable(feature = "const_vec_new")]