diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 932c0eaa4c7..7ec75ed0114 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -473,6 +473,7 @@ assert_eq!(m, ", $reversed, ");
             #[unstable(feature = "reverse_bits", issue = "48763")]
             #[rustc_const_unstable(feature = "const_int_conversion")]
             #[inline]
+            #[must_use]
             pub const fn reverse_bits(self) -> Self {
                 (self as $UnsignedT).reverse_bits() as Self
             }
@@ -2522,6 +2523,7 @@ assert_eq!(m, ", $reversed, ");
 ```"),
             #[unstable(feature = "reverse_bits", issue = "48763")]
             #[inline]
+            #[must_use]
             pub const fn reverse_bits(self) -> Self {
                 intrinsics::bitreverse(self as $ActualT) as Self
             }
diff --git a/src/libcore/num/wrapping.rs b/src/libcore/num/wrapping.rs
index a3491bc3dc6..5eb5ec558f8 100644
--- a/src/libcore/num/wrapping.rs
+++ b/src/libcore/num/wrapping.rs
@@ -524,6 +524,7 @@ assert_eq!(n.trailing_zeros(), 3);
             /// ```
             #[unstable(feature = "reverse_bits", issue = "48763")]
             #[inline]
+            #[must_use]
             pub const fn reverse_bits(self) -> Self {
                 Wrapping(self.0.reverse_bits())
             }