diff --git a/components/locale_core/src/parser/mod.rs b/components/locale_core/src/parser/mod.rs
index a5a8ae24328..4000b8f241a 100644
--- a/components/locale_core/src/parser/mod.rs
+++ b/components/locale_core/src/parser/mod.rs
@@ -24,25 +24,27 @@ const fn is_separator(slice: &[u8], idx: usize) -> bool {
     b == b'-' || b == b'_'
 }
 
-const fn get_current_subtag(slice: &[u8], idx: usize) -> (usize, usize) {
+const fn get_current_subtag(mut slice: &[u8], idx: usize) -> (&[u8], &[u8]) {
     debug_assert!(idx < slice.len());
 
     // This function is called only on the idx == 0 or on a separator.
-    let (start, mut end) = if is_separator(slice, idx) {
-        // If it's a separator, set the start to idx+1 and advance the idx to the next char.
-        (idx + 1, idx + 1)
+    let mut end = if is_separator(slice, idx) {
+        // If it's a separator, skip it
+        slice = slice.split_at(idx + 1).1;
+        0
     } else {
-        // If it's idx=0, start is 0 and end is set to 1
+        // If it's idx=0, end is set to 1
         debug_assert!(idx == 0);
-        (0, 1)
+        1
     };
 
     while end < slice.len() && !is_separator(slice, end) {
         // Advance until we reach end of slice or a separator.
         end += 1;
     }
-    // Notice: this slice may be empty (start == end) for cases like `"en-"` or `"en--US"`
-    (start, end)
+
+    // Notice: this slice may be empty (end == 0) for cases like `"en-"` or `"en--US"`
+    (slice, slice.split_at(end).0)
 }
 
 // `SubtagIterator` is a helper iterator for [`LanguageIdentifier`] and [`Locale`] parsing.
@@ -59,25 +61,25 @@ const fn get_current_subtag(slice: &[u8], idx: usize) -> (usize, usize) {
 // All methods return an `Option` of a `Result`.
 #[derive(Copy, Clone, Debug)]
 pub struct SubtagIterator<'a> {
-    pub slice: &'a [u8],
+    remaining: &'a [u8],
     done: bool,
-    // done + subtag is faster than Option<(usize, usize)>
+    // done + current is faster than Option<&[u8]>
     // at the time of writing.
-    subtag: (usize, usize),
+    current: &'a [u8],
 }
 
 impl<'a> SubtagIterator<'a> {
     pub const fn new(slice: &'a [u8]) -> Self {
-        let subtag = if slice.is_empty() || is_separator(slice, 0) {
+        let (remaining, current) = if slice.is_empty() || is_separator(slice, 0) {
             // This returns (0, 0) which returns Some(b"") for slices like `"-en"` or `"-"`
-            (0, 0)
+            (slice, b"".as_slice())
         } else {
             get_current_subtag(slice, 0)
         };
         Self {
-            slice,
+            remaining,
             done: false,
-            subtag,
+            current,
         }
     }
 
@@ -85,29 +87,22 @@ impl<'a> SubtagIterator<'a> {
         if self.done {
             return (self, None);
         }
-        let result = self.subtag;
-        if result.1 < self.slice.len() {
-            self.subtag = get_current_subtag(self.slice, result.1);
+        let result = self.current;
+        if self.current.len() < self.remaining.len() {
+            let (remaining, current) = get_current_subtag(self.remaining, self.current.len());
+            self.remaining = remaining;
+            self.current = current;
         } else {
             self.done = true;
         }
-        (
-            self,
-            Some(self.slice.split_at(result.1).0.split_at(result.0).1),
-        )
+        (self, Some(result))
     }
 
     pub const fn peek(&self) -> Option<&'a [u8]> {
         if self.done {
             return None;
         }
-        Some(
-            self.slice
-                .split_at(self.subtag.1)
-                .0
-                .split_at(self.subtag.0)
-                .1,
-        )
+        Some(self.current)
     }
 }
 
@@ -193,42 +188,42 @@ mod test {
     fn get_current_subtag_test() {
         let slice = "-";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (1, 1));
+        assert_eq!(current, (b"".as_slice(), b"".as_slice()));
 
         let slice = "-en";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (1, 3));
+        assert_eq!(current, (b"en".as_slice(), b"en".as_slice()));
 
         let slice = "-en-";
         let current = get_current_subtag(slice.as_bytes(), 3);
-        assert_eq!(current, (4, 4));
+        assert_eq!(current, (b"".as_slice(), b"".as_slice()));
 
         let slice = "en-";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (0, 2));
+        assert_eq!(current, (b"en-".as_slice(), b"en".as_slice()));
 
         let current = get_current_subtag(slice.as_bytes(), 2);
-        assert_eq!(current, (3, 3));
+        assert_eq!(current, (b"".as_slice(), b"".as_slice()));
 
         let slice = "en--US";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (0, 2));
+        assert_eq!(current, (b"en--US".as_slice(), b"en".as_slice()));
 
         let current = get_current_subtag(slice.as_bytes(), 2);
-        assert_eq!(current, (3, 3));
+        assert_eq!(current, (b"-US".as_slice(), b"".as_slice()));
 
         let current = get_current_subtag(slice.as_bytes(), 3);
-        assert_eq!(current, (4, 6));
+        assert_eq!(current, (b"US".as_slice(), b"US".as_slice()));
 
         let slice = "--";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (1, 1));
+        assert_eq!(current, (b"-".as_slice(), b"".as_slice()));
 
         let current = get_current_subtag(slice.as_bytes(), 1);
-        assert_eq!(current, (2, 2));
+        assert_eq!(current, (b"".as_slice(), b"".as_slice()));
 
         let slice = "-";
         let current = get_current_subtag(slice.as_bytes(), 0);
-        assert_eq!(current, (1, 1));
+        assert_eq!(current, (b"".as_slice(), b"".as_slice()));
     }
 }