diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index 7c38d830636d..f6cef3f80670 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -704,7 +704,8 @@ impl f32 {
     /// [`INFINITY`]: Self::INFINITY
     /// [`MIN`]: Self::MIN
     /// [`MAX`]: Self::MAX
-    #[unstable(feature = "float_next_up_down", issue = "none")]
+    #[unstable(feature = "float_next_up_down", issue = "91399")]
+    #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
     pub const fn next_up(self) -> Self {
         // We must use strictly integer arithmetic to prevent denormals from
         // flushing to zero after an arithmetic operation on some platforms.
@@ -753,7 +754,8 @@ impl f32 {
     /// [`INFINITY`]: Self::INFINITY
     /// [`MIN`]: Self::MIN
     /// [`MAX`]: Self::MAX
-    #[unstable(feature = "float_next_up_down", issue = "none")]
+    #[unstable(feature = "float_next_up_down", issue = "91399")]
+    #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
     pub const fn next_down(self) -> Self {
         // We must use strictly integer arithmetic to prevent denormals from
         // flushing to zero after an arithmetic operation on some platforms.
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index 8146f0075316..328b19b203c2 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -714,7 +714,8 @@ impl f64 {
     /// [`INFINITY`]: Self::INFINITY
     /// [`MIN`]: Self::MIN
     /// [`MAX`]: Self::MAX
-    #[unstable(feature = "float_next_up_down", issue = "none")]
+    #[unstable(feature = "float_next_up_down", issue = "91399")]
+    #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
     pub const fn next_up(self) -> Self {
         // We must use strictly integer arithmetic to prevent denormals from
         // flushing to zero after an arithmetic operation on some platforms.
@@ -763,7 +764,8 @@ impl f64 {
     /// [`INFINITY`]: Self::INFINITY
     /// [`MIN`]: Self::MIN
     /// [`MAX`]: Self::MAX
-    #[unstable(feature = "float_next_up_down", issue = "none")]
+    #[unstable(feature = "float_next_up_down", issue = "91399")]
+    #[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
     pub const fn next_down(self) -> Self {
         // We must use strictly integer arithmetic to prevent denormals from
         // flushing to zero after an arithmetic operation on some platforms.