diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index 78c4966c6f9e..cd4b32735e57 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -380,6 +380,15 @@ pub enum ClearCrossCrate<T> {
     Set(T),
 }
 
+impl<T> ClearCrossCrate<T> {
+    pub fn assert_crate_local(self) -> T {
+        match self {
+            ClearCrossCrate::Clear => bug!("unwrapping cross-crate data"),
+            ClearCrossCrate::Set(v) => v,
+        }
+    }
+}
+
 impl<T: serialize::Encodable> serialize::UseSpecializedEncodable for ClearCrossCrate<T> {}
 impl<T: serialize::Decodable> serialize::UseSpecializedDecodable for ClearCrossCrate<T> {}