diff --git a/compiler/rustc_lexer/src/unescape.rs b/compiler/rustc_lexer/src/unescape.rs
index d98a702427e..ddbe826f570 100644
--- a/compiler/rustc_lexer/src/unescape.rs
+++ b/compiler/rustc_lexer/src/unescape.rs
@@ -169,8 +169,9 @@ pub fn in_double_quotes(self) -> bool {
     /// Non-byte literals should have `\xXX` escapes that are within the ASCII range.
     fn ascii_escapes_should_be_ascii(self) -> bool {
         match self {
-            Mode::Char | Mode::Str | Mode::RawStr => true,
-            Mode::Byte | Mode::ByteStr | Mode::RawByteStr | Mode::CStr | Mode::RawCStr => false,
+            Mode::Char | Mode::Str => true,
+            Mode::Byte | Mode::ByteStr | Mode::CStr => false,
+            Mode::RawStr | Mode::RawByteStr | Mode::RawCStr => unreachable!(),
         }
     }