diff --git a/src/descriptors.rs b/src/descriptors.rs
index eadf427..ab9e6c6 100644
--- a/src/descriptors.rs
+++ b/src/descriptors.rs
@@ -7,20 +7,22 @@ use std::{
 
 use crate::ParseError;
 
-// Returns the unqualified segment and the following char ('/', ';', or None)
-// or an error. This only extracts the unqualified segment at the start of
-// the given data, and ignores anything following.
-fn parse_unqualified_segment(data: &str) -> Result<(&str, Option<char>), ParseError> {
+// Returns the length of the unqualified segment and the following char
+// ('/', ';', or None) or an error. This only extracts the unqualified
+// segment at the start of the given data, and ignores anything following.
+// Returns None if no unqualified segment terminator was found.
+#[inline(always)]
+fn parse_unqualified_segment(data: &str) -> Result<Option<(usize, char)>, ParseError> {
     for (ix, c) in data.char_indices() {
         match c {
             '/' if ix == 0 => fail!("Unexpected '/' at start of unqualified segment"),
             ';' if ix == 0 => fail!("Unexpected ';' at start of unqualified segment"),
-            '/' | ';' => return Ok((&data[0..ix], Some(c))),
+            '/' | ';' => return Ok(Some((ix, c))),
             '.' | '[' | '<' | '>' => fail!("Disallowed character in unqualified segment"),
             _ => (),
         };
     }
-    Ok((data, None))
+    Ok(None)
 }
 
 /// Represents a valid binary class or interface name in the syntax of
@@ -36,9 +38,9 @@ impl<'a> TryFrom<Cow<'a, str>> for ClassName<'a> {
         let mut index = 0;
         loop {
             match parse_unqualified_segment(&value[index..])? {
-                (_, None) => break,
-                (_, Some(';')) => fail!("Disallowed ';' in class name"),
-                (segment, Some('/')) => index += segment.len() + 1,
+                None => break,
+                Some((_, ';')) => fail!("Disallowed ';' in class name"),
+                Some((segment_len, '/')) => index += segment_len + 1,
                 _ => panic!("Got unexpected return value from parse_unqualified_segment"),
             }
         }
@@ -81,18 +83,16 @@ fn parse_class_descriptor<'a>(
     let mut next_index = index;
     loop {
         match parse_unqualified_segment(&data[next_index..])? {
-            (segment, Some(';')) => {
+            Some((segment_len, ';')) => {
                 return Ok(ClassName(match data {
-                    Cow::Borrowed(data) => {
-                        Cow::Borrowed(&data[index..(next_index + segment.len())])
-                    }
+                    Cow::Borrowed(data) => Cow::Borrowed(&data[index..(next_index + segment_len)]),
                     Cow::Owned(data) => {
-                        Cow::Owned(data[index..(next_index + segment.len())].to_string())
+                        Cow::Owned(data[index..(next_index + segment_len)].to_string())
                     }
                 }))
             }
-            (segment, Some('/')) => next_index += segment.len() + 1,
-            (_, None) => fail!("Unterminated unqualified segment"),
+            Some((segment_len, '/')) => next_index += segment_len + 1,
+            None => fail!("Unterminated unqualified segment"),
             _ => panic!("Got unexpected return value from parse_unqualified_segment"),
         }
     }