3 files changed, 32 insertions, 10 deletions
diff --git a/src/libstd/env.rs b/src/libstd/env.rs
index 6956dc0d901..01bc733d440 100644
--- a/src/libstd/env.rs
+++ b/src/libstd/env.rs
@@ -587,6 +587,13 @@ impl ExactSizeIterator for Args {
     fn len(&self) -> usize { self.inner.len() }
 }
 
+#[stable(feature = "env_iterators", since = "1.11.0")]
+impl DoubleEndedIterator for Args {
+    fn next_back(&mut self) -> Option<String> {
+        self.inner.next_back().map(|s| s.into_string().unwrap())
+    }
+}
+
 #[stable(feature = "env", since = "1.0.0")]
 impl Iterator for ArgsOs {
     type Item = OsString;
@@ -599,6 +606,10 @@ impl ExactSizeIterator for ArgsOs {
     fn len(&self) -> usize { self.inner.len() }
 }
 
+#[stable(feature = "env_iterators", since = "1.11.0")]
+impl DoubleEndedIterator for ArgsOs {
+    fn next_back(&mut self) -> Option<OsString> { self.inner.next_back() }
+}
 /// Constants associated with the current target
 #[stable(feature = "env", since = "1.0.0")]
 pub mod consts {
diff --git a/src/libstd/sys/unix/os.rs b/src/libstd/sys/unix/os.rs
index 21ce6b19ceb..a8cb1ce49d2 100644
--- a/src/libstd/sys/unix/os.rs
+++ b/src/libstd/sys/unix/os.rs
@@ -308,6 +308,10 @@ impl ExactSizeIterator for Args {
     fn len(&self) -> usize { self.iter.len() }
 }
 
+impl DoubleEndedIterator for Args {
+    fn next_back(&mut self) -> Option<OsString> { self.iter.next_back() }
+}
+
 /// Returns the command line arguments
 ///
 /// Returns a list of the command line arguments.
diff --git a/src/libstd/sys/windows/os.rs b/src/libstd/sys/windows/os.rs
index 32ca32e76cb..0cea7f81e36 100644
--- a/src/libstd/sys/windows/os.rs
+++ b/src/libstd/sys/windows/os.rs
@@ -278,23 +278,30 @@ pub struct Args {
     cur: *mut *mut u16,
 }
 
+unsafe fn os_string_from_ptr(ptr: *mut u16) -> OsString {
+    let mut len = 0;
+    while *ptr.offset(len) != 0 { len += 1; }
+
+    // Push it onto the list.
+    let ptr = ptr as *const u16;
+    let buf = slice::from_raw_parts(ptr, len as usize);
+    OsStringExt::from_wide(buf)
+}
+
 impl Iterator for Args {
     type Item = OsString;
     fn next(&mut self) -> Option<OsString> {
-        self.range.next().map(|i| unsafe {
-            let ptr = *self.cur.offset(i);
-            let mut len = 0;
-            while *ptr.offset(len) != 0 { len += 1; }
-
-            // Push it onto the list.
-            let ptr = ptr as *const u16;
-            let buf = slice::from_raw_parts(ptr, len as usize);
-            OsStringExt::from_wide(buf)
-        })
+        self.range.next().map(|i| unsafe { os_string_from_ptr(*self.cur.offset(i)) } )
     }
     fn size_hint(&self) -> (usize, Option<usize>) { self.range.size_hint() }
 }
 
+impl DoubleEndedIterator for Args {
+    fn next_back(&mut self) -> Option<OsString> {
+        self.range.next_back().map(|i| unsafe { os_string_from_ptr(*self.cur.offset(i)) } )
+    }
+}
+
 impl ExactSizeIterator for Args {
     fn len(&self) -> usize { self.range.len() }
 }