diff --git a/library/core/src/str/iter.rs b/library/core/src/str/iter.rs
index 0c74f6e45a78..83f484dc570c 100644
--- a/library/core/src/str/iter.rs
+++ b/library/core/src/str/iter.rs
@@ -47,7 +47,7 @@ impl<'a> Iterator for Chars<'a> {
     #[inline]
     fn count(self) -> usize {
         // length in `char` is equal to the number of non-continuation bytes
-        self.iter.map(|&byte| !utf8_is_cont_byte(byte) as usize).sum()
+        self.iter.filter(|&&byte| !utf8_is_cont_byte(byte)).count()
     }
 
     #[inline]