diff --git a/src/args/arg_matches.rs b/src/args/arg_matches.rs
index 5617b226462..7ac112877ec 100644
--- a/src/args/arg_matches.rs
+++ b/src/args/arg_matches.rs
@@ -855,6 +855,8 @@ impl<'a> DoubleEndedIterator for OsValues<'a> {
     fn next_back(&mut self) -> Option<&'a OsStr> { self.iter.next_back() }
 }
 
+impl<'a> ExactSizeIterator for OsValues<'a> {}
+
 /// Creates an empty iterator.
 impl<'a> Default for OsValues<'a> {
     fn default() -> Self {