diff --git a/core-foundation-sys/src/lib.rs b/core-foundation-sys/src/lib.rs
index b39da97..96c0b1e 100644
--- a/core-foundation-sys/src/lib.rs
+++ b/core-foundation-sys/src/lib.rs
@@ -8,6 +8,8 @@
 // except according to those terms.
 #![allow(non_snake_case, non_camel_case_types, non_upper_case_globals, improper_ctypes)]
 
+#![cfg_attr(all(feature="mac_os_10_7_support", feature="mac_os_10_8_features"), feature(linkage))] // back-compat requires weak linkage
+
 extern crate libc;
 
 pub mod array;
diff --git a/core-foundation-sys/src/url.rs b/core-foundation-sys/src/url.rs
index c0f8282..a9049f8 100644
--- a/core-foundation-sys/src/url.rs
+++ b/core-foundation-sys/src/url.rs
@@ -72,10 +72,13 @@ extern {
     pub static kCFURLParentDirectoryURLKey: CFStringRef;
     pub static kCFURLPreferredIOBlockSizeKey: CFStringRef;
     pub static kCFURLTypeIdentifierKey: CFStringRef;
-    // static kCFURLVolumeIdentifierKey: CFStringRef;
-    // static kCFURLVolumeURLKey: CFStringRef;
-    // static kCFURLIsExcludedFromBackupKey: CFStringRef;
-    // static kCFURLFileResourceTypeKey: CFStringRef;
+    pub static kCFURLVolumeIdentifierKey: CFStringRef;
+    pub static kCFURLVolumeURLKey: CFStringRef;
+
+    #[cfg(feature="mac_os_10_8_features")]
+    #[cfg_attr(feature = "mac_os_10_7_support", linkage = "extern_weak")]
+    pub static kCFURLIsExcludedFromBackupKey: CFStringRef;
+    pub static kCFURLFileResourceTypeKey: CFStringRef;
 
     /* Creating a CFURL */
     pub fn CFURLCopyAbsoluteURL(anURL: CFURLRef) -> CFURLRef;
@@ -151,3 +154,9 @@ extern {
     //fn CFURLStartAccessingSecurityScopedResource
     //fn CFURLStopAccessingSecurityScopedResource
 }
+
+#[test]
+#[cfg(feature="mac_os_10_8_features")]
+fn can_see_excluded_from_backup_key() {
+    let _ = unsafe { kCFURLIsExcludedFromBackupKey };
+}