diff --git a/library/core/src/slice/ascii.rs b/library/core/src/slice/ascii.rs
index e17a2e03d2dc..42916558b5fc 100644
--- a/library/core/src/slice/ascii.rs
+++ b/library/core/src/slice/ascii.rs
@@ -9,6 +9,8 @@
 
 impl [u8] {
     /// Checks if all bytes in this slice are within the ASCII range.
+    ///
+    /// An empty slice returns `true`.
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[rustc_const_stable(feature = "const_slice_is_ascii", since = "1.74.0")]
     #[must_use]
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index 3a5efa7d8351..82019b9b3afe 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -2704,6 +2704,8 @@ pub fn parse<F: FromStr>(&self) -> Result<F, F::Err> {
 
     /// Checks if all characters in this string are within the ASCII range.
     ///
+    /// An empty string returns `true`.
+    ///
     /// # Examples
     ///
     /// ```
diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index 6c098034eea3..09bd911aa769 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -1215,6 +1215,8 @@ pub fn to_ascii_uppercase(&self) -> OsString {
 
     /// Checks if all characters in this string are within the ASCII range.
     ///
+    /// An empty string returns `true`.
+    ///
     /// # Examples
     ///
     /// ```