diff --git a/core/parser/src/source/utf8.rs b/core/parser/src/source/utf8.rs
index f5e96f44cb4..41c8404b1c5 100644
--- a/core/parser/src/source/utf8.rs
+++ b/core/parser/src/source/utf8.rs
@@ -28,27 +28,26 @@ impl<R: Read> ReadChar for UTF8Input<R> {
     fn next_char(&mut self) -> io::Result<Option<u32>> {
         // Decode UTF-8
         let x = match self.next_byte()? {
-            Some(b) if b < 128 => return Ok(Some(u32::from(b))),
-            Some(b) => b,
-            None => return Ok(None),
+            Some(b) if b >= 128 => b,         // UTF-8 codepoint
+            b => return Ok(b.map(u32::from)), // ASCII or None
         };
 
         // Multibyte case follows
         // Decode from a byte combination out of: [[[x y] z] w]
         // NOTE: Performance is sensitive to the exact formulation here
         let init = utf8_first_byte(x, 2);
-        let y = unwrap_or_0(self.next_byte()?);
+        let y = self.next_byte()?.unwrap_or(0);
         let mut ch = utf8_acc_cont_byte(init, y);
         if x >= 0xE0 {
             // [[x y z] w] case
             // 5th bit in 0xE0 .. 0xEF is always clear, so `init` is still valid
-            let z = unwrap_or_0(self.next_byte()?);
+            let z = self.next_byte()?.unwrap_or(0);
             let y_z = utf8_acc_cont_byte(u32::from(y & CONT_MASK), z);
             ch = init << 12 | y_z;
             if x >= 0xF0 {
                 // [x y z w] case
                 // use only the lower 3 bits of `init`
-                let w = unwrap_or_0(self.next_byte()?);
+                let w = self.next_byte()?.unwrap_or(0);
                 ch = (init & 7) << 18 | utf8_acc_cont_byte(y_z, w);
             }
         };
@@ -71,7 +70,3 @@ fn utf8_first_byte(byte: u8, width: u32) -> u32 {
 fn utf8_acc_cont_byte(ch: u32, byte: u8) -> u32 {
     (ch << 6) | u32::from(byte & CONT_MASK)
 }
-
-fn unwrap_or_0(opt: Option<u8>) -> u8 {
-    opt.unwrap_or(0)
-}