diff --git a/js/public/CharacterEncoding.h b/js/public/CharacterEncoding.h
index 6d8ca12a14f2..21fe34012994 100644
--- a/js/public/CharacterEncoding.h
+++ b/js/public/CharacterEncoding.h
@@ -40,6 +40,20 @@ class Latin1Chars : public mozilla::Range<Latin1Char> {
              aLength) {}
 };
 
+/*
+ * Like Latin1Chars, but the chars are const.
+ */
+class ConstLatin1Chars : public mozilla::Range<const Latin1Char> {
+  typedef mozilla::Range<const Latin1Char> Base;
+
+ public:
+  using CharT = Latin1Char;
+
+  ConstLatin1Chars() = default;
+  ConstLatin1Chars(const Latin1Char* aChars, size_t aLength)
+      : Base(aChars, aLength) {}
+};
+
 /*
  * A Latin1Chars, but with \0 termination for C compatibility.
  */