diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index b6b9a33aede..02cc0f9d770 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -320,7 +320,7 @@ pub const fn from_digit(num: u32, radix: u32) -> Option<char> {
     /// '1'.is_digit(37);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_char_is_digit", issue = "132241")]
+    #[rustc_const_unstable(feature = "const_char_classify", issue = "132241")]
     #[inline]
     pub const fn is_digit(self, radix: u32) -> bool {
         self.to_digit(radix).is_some()
@@ -856,8 +856,9 @@ pub const fn is_uppercase(self) -> bool {
     /// ```
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_char_classify", issue = "132241")]
     #[inline]
-    pub fn is_whitespace(self) -> bool {
+    pub const fn is_whitespace(self) -> bool {
         match self {
             ' ' | '\x09'..='\x0d' => true,
             c => c > '\x7f' && unicode::White_Space(c),
diff --git a/library/core/src/unicode/unicode_data.rs b/library/core/src/unicode/unicode_data.rs
index 839f06ab84d..4655d35e9c4 100644
--- a/library/core/src/unicode/unicode_data.rs
+++ b/library/core/src/unicode/unicode_data.rs
@@ -572,7 +572,7 @@ pub mod white_space {
         0, 0, 0, 0, 0, 0, 0, 0, 0,
     ];
     #[inline]
-    pub fn lookup(c: char) -> bool {
+    pub const fn lookup(c: char) -> bool {
         match c as u32 >> 8 {
             0 => WHITESPACE_MAP[c as usize & 0xff] & 1 != 0,
             22 => c as u32 == 0x1680,
diff --git a/src/tools/unicode-table-generator/src/cascading_map.rs b/src/tools/unicode-table-generator/src/cascading_map.rs
index 036f0bd7eac..1eb35e819c0 100644
--- a/src/tools/unicode-table-generator/src/cascading_map.rs
+++ b/src/tools/unicode-table-generator/src/cascading_map.rs
@@ -65,7 +65,7 @@ pub fn emit_cascading_map(&mut self, ranges: &[Range<u32>]) -> bool {
         self.bytes_used += 256;
 
         writeln!(&mut self.file, "#[inline]").unwrap();
-        writeln!(&mut self.file, "pub fn lookup(c: char) -> bool {{").unwrap();
+        writeln!(&mut self.file, "pub const fn lookup(c: char) -> bool {{").unwrap();
         writeln!(&mut self.file, "    match c as u32 >> 8 {{").unwrap();
         for arm in arms {
             writeln!(&mut self.file, "        {},", arm).unwrap();