diff --git a/library/alloc/tests/str.rs b/library/alloc/tests/str.rs
index 4d182be02c9..c1dbbde08b6 100644
--- a/library/alloc/tests/str.rs
+++ b/library/alloc/tests/str.rs
@@ -1499,13 +1499,25 @@ fn test_split_whitespace() {
 
 #[test]
 fn test_lines() {
-    let data = "\nMäry häd ä little lämb\n\r\nLittle lämb\n";
-    let lines: Vec<&str> = data.lines().collect();
-    assert_eq!(lines, ["", "Märy häd ä little lämb", "", "Little lämb"]);
-
-    let data = "\r\nMäry häd ä little lämb\n\nLittle lämb"; // no trailing \n
-    let lines: Vec<&str> = data.lines().collect();
-    assert_eq!(lines, ["", "Märy häd ä little lämb", "", "Little lämb"]);
+    fn t(data: &str, expected: &[&str]) {
+        let lines: Vec<&str> = data.lines().collect();
+        assert_eq!(lines, expected);
+    }
+    t("", &[]);
+    t("\n", &[""]);
+    t("\n2nd", &["", "2nd"]);
+    t("\r\n", &[""]);
+    t("bare\r", &["bare\r"]);
+    t("bare\rcr", &["bare\rcr"]);
+    t("Text\n\r", &["Text", "\r"]);
+    t(
+        "\nMäry häd ä little lämb\n\r\nLittle lämb\n",
+        &["", "Märy häd ä little lämb", "", "Little lämb"],
+    );
+    t(
+        "\r\nMäry häd ä little lämb\n\nLittle lämb",
+        &["", "Märy häd ä little lämb", "", "Little lämb"],
+    );
 }
 
 #[test]
diff --git a/library/core/src/str/iter.rs b/library/core/src/str/iter.rs
index 95c682f42d0..772c3605562 100644
--- a/library/core/src/str/iter.rs
+++ b/library/core/src/str/iter.rs
@@ -13,7 +13,7 @@
 use super::pattern::Pattern;
 use super::pattern::{DoubleEndedSearcher, ReverseSearcher, Searcher};
 use super::validations::{next_code_point, next_code_point_reverse};
-use super::LinesAnyMap;
+use super::LinesMap;
 use super::{BytesIsNotEmpty, UnsafeBytesToStr};
 use super::{CharEscapeDebugContinue, CharEscapeDefault, CharEscapeUnicode};
 use super::{IsAsciiWhitespace, IsNotEmpty, IsWhitespace};
@@ -1104,7 +1104,7 @@ fn next_back(&mut self) -> Option<&'a str>
 #[stable(feature = "rust1", since = "1.0.0")]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[derive(Clone, Debug)]
-pub struct Lines<'a>(pub(super) Map<SplitTerminator<'a, char>, LinesAnyMap>);
+pub struct Lines<'a>(pub(super) Map<SplitInclusive<'a, char>, LinesMap>);
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Iterator for Lines<'a> {
diff --git a/library/core/src/str/mod.rs b/library/core/src/str/mod.rs
index ab2f8520ecb..2b23f64732b 100644
--- a/library/core/src/str/mod.rs
+++ b/library/core/src/str/mod.rs
@@ -1011,7 +1011,7 @@ pub fn split_ascii_whitespace(&self) -> SplitAsciiWhitespace<'_> {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn lines(&self) -> Lines<'_> {
-        Lines(self.split_terminator('\n').map(LinesAnyMap))
+        Lines(self.split_inclusive('\n').map(LinesMap))
     }
 
     /// An iterator over the lines of a string.
@@ -2604,10 +2604,10 @@ fn default() -> Self {
 impl_fn_for_zst! {
     /// A nameable, cloneable fn type
     #[derive(Clone)]
-    struct LinesAnyMap impl<'a> Fn = |line: &'a str| -> &'a str {
-        let l = line.len();
-        if l > 0 && line.as_bytes()[l - 1] == b'\r' { &line[0 .. l - 1] }
-        else { line }
+    struct LinesMap impl<'a> Fn = |line: &'a str| -> &'a str {
+        let Some(line) = line.strip_suffix('\n') else { return line };
+        let Some(line) = line.strip_suffix('\r') else { return line };
+        line
     };
 
     #[derive(Clone)]