diff --git a/src/libsyntax/ptr.rs b/src/libsyntax/ptr.rs
index ed10857e4c56..25d916af77d2 100644
--- a/src/libsyntax/ptr.rs
+++ b/src/libsyntax/ptr.rs
@@ -95,16 +95,6 @@ impl<T: 'static> P<T> {
     }
 }
 
-impl<T: 'static> P<[T]> {
-    pub fn map_slice<F>(self, f: F) -> P<[T]> where
-        F: FnOnce(Vec<T>) -> Vec<T>
-    {
-        P {
-            ptr: f(self.ptr.into()).into(),
-        }
-    }
-}
-
 impl<T: ?Sized> Deref for P<T> {
     type Target = T;