diff --git a/library/alloc/src/collections/btree/borrow.rs b/library/alloc/src/collections/btree/borrow.rs
index 5c95acfbe9c20..016f139a501a0 100644
--- a/library/alloc/src/collections/btree/borrow.rs
+++ b/library/alloc/src/collections/btree/borrow.rs
@@ -16,6 +16,9 @@ pub struct DormantMutRef<'a, T> {
     _marker: PhantomData<&'a mut T>,
 }
 
+unsafe impl<'a, T> Sync for DormantMutRef<'a, T> where &'a mut T: Sync {}
+unsafe impl<'a, T> Send for DormantMutRef<'a, T> where &'a mut T: Send {}
+
 impl<'a, T> DormantMutRef<'a, T> {
     /// Capture a unique borrow, and immediately reborrow it. For the compiler,
     /// the lifetime of the new reference is the same as the lifetime of the
diff --git a/library/alloc/src/collections/btree/map/tests.rs b/library/alloc/src/collections/btree/map/tests.rs
index af5cf7d7d875c..d2cd6b8e5241a 100644
--- a/library/alloc/src/collections/btree/map/tests.rs
+++ b/library/alloc/src/collections/btree/map/tests.rs
@@ -1418,6 +1418,146 @@ fn test_variance() {
     }
 }
 
+#[test]
+#[allow(dead_code)]
+fn test_sync() {
+    fn map<T: Sync>(v: &BTreeMap<T, T>) -> impl Sync + '_ {
+        v
+    }
+
+    fn into_iter<T: Sync>(v: BTreeMap<T, T>) -> impl Sync {
+        v.into_iter()
+    }
+
+    fn into_keys<T: Sync + Ord>(v: BTreeMap<T, T>) -> impl Sync {
+        v.into_keys()
+    }
+
+    fn into_values<T: Sync + Ord>(v: BTreeMap<T, T>) -> impl Sync {
+        v.into_values()
+    }
+
+    fn drain_filter<T: Sync + Ord>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        v.drain_filter(|_, _| false)
+    }
+
+    fn iter<T: Sync>(v: &BTreeMap<T, T>) -> impl Sync + '_ {
+        v.iter()
+    }
+
+    fn iter_mut<T: Sync>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        v.iter_mut()
+    }
+
+    fn keys<T: Sync>(v: &BTreeMap<T, T>) -> impl Sync + '_ {
+        v.keys()
+    }
+
+    fn values<T: Sync>(v: &BTreeMap<T, T>) -> impl Sync + '_ {
+        v.values()
+    }
+
+    fn values_mut<T: Sync>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        v.values_mut()
+    }
+
+    fn range<T: Sync + Ord>(v: &BTreeMap<T, T>) -> impl Sync + '_ {
+        v.range(..)
+    }
+
+    fn range_mut<T: Sync + Ord>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        v.range_mut(..)
+    }
+
+    fn entry<T: Sync + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        v.entry(Default::default())
+    }
+
+    fn occupied_entry<T: Sync + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        match v.entry(Default::default()) {
+            Occupied(entry) => entry,
+            _ => unreachable!(),
+        }
+    }
+
+    fn vacant_entry<T: Sync + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Sync + '_ {
+        match v.entry(Default::default()) {
+            Vacant(entry) => entry,
+            _ => unreachable!(),
+        }
+    }
+}
+
+#[test]
+#[allow(dead_code)]
+fn test_send() {
+    fn map<T: Send>(v: BTreeMap<T, T>) -> impl Send {
+        v
+    }
+
+    fn into_iter<T: Send>(v: BTreeMap<T, T>) -> impl Send {
+        v.into_iter()
+    }
+
+    fn into_keys<T: Send + Ord>(v: BTreeMap<T, T>) -> impl Send {
+        v.into_keys()
+    }
+
+    fn into_values<T: Send + Ord>(v: BTreeMap<T, T>) -> impl Send {
+        v.into_values()
+    }
+
+    fn drain_filter<T: Send + Ord>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        v.drain_filter(|_, _| false)
+    }
+
+    fn iter<T: Send + Sync>(v: &BTreeMap<T, T>) -> impl Send + '_ {
+        v.iter()
+    }
+
+    fn iter_mut<T: Send + Sync>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        v.iter_mut()
+    }
+
+    fn keys<T: Send + Sync>(v: &BTreeMap<T, T>) -> impl Send + '_ {
+        v.keys()
+    }
+
+    fn values<T: Send + Sync>(v: &BTreeMap<T, T>) -> impl Send + '_ {
+        v.values()
+    }
+
+    fn values_mut<T: Send + Sync>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        v.values_mut()
+    }
+
+    fn range<T: Send + Sync + Ord>(v: &BTreeMap<T, T>) -> impl Send + '_ {
+        v.range(..)
+    }
+
+    fn range_mut<T: Send + Sync + Ord>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        v.range_mut(..)
+    }
+
+    fn entry<T: Send + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        v.entry(Default::default())
+    }
+
+    fn occupied_entry<T: Send + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        match v.entry(Default::default()) {
+            Occupied(entry) => entry,
+            _ => unreachable!(),
+        }
+    }
+
+    fn vacant_entry<T: Send + Ord + Default>(v: &mut BTreeMap<T, T>) -> impl Send + '_ {
+        match v.entry(Default::default()) {
+            Vacant(entry) => entry,
+            _ => unreachable!(),
+        }
+    }
+}
+
 #[test]
 fn test_occupied_entry_key() {
     let mut a = BTreeMap::new();