diff --git a/library/alloc/src/collections/btree/map.rs b/library/alloc/src/collections/btree/map.rs
index 271ea88fff6..58ffa9710d3 100644
--- a/library/alloc/src/collections/btree/map.rs
+++ b/library/alloc/src/collections/btree/map.rs
@@ -180,7 +180,7 @@ pub struct BTreeMap<
     /// `ManuallyDrop` to control drop order (needs to be dropped after all the nodes).
     pub(super) alloc: ManuallyDrop<A>,
     // For dropck; the `Box` avoids making the `Unpin` impl more strict than before
-    _marker: PhantomData<crate::boxed::Box<(K, V)>>,
+    _marker: PhantomData<crate::boxed::Box<(K, V), A>>,
 }
 
 #[stable(feature = "btree_drop", since = "1.7.0")]