diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index 1b5e44a913467..8b38e6fc259af 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/alloc/src/boxed.rs
@@ -1115,6 +1115,8 @@ impl<T: ?Sized> Box<T> {
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same `NonNull` pointer.
     ///
+    /// The non-null pointer must point to a block of memory allocated by the global allocator.
+    ///
     /// The safety conditions are described in the [memory layout] section.
     ///
     /// # Examples
@@ -1170,7 +1172,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same raw pointer.
     ///
-    /// The raw pointer must point to a block of memory allocated by `alloc`
+    /// The raw pointer must point to a block of memory allocated by `alloc`.
     ///
     /// # Examples
     ///
@@ -1225,6 +1227,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same raw pointer.
     ///
+    /// The non-null pointer must point to a block of memory allocated by `alloc`.
     ///
     /// # Examples
     ///
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 8eee7cff2080d..431e19e6ef1d7 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -2740,7 +2740,7 @@ impl<T: ?Sized> Weak<T> {
     /// # Safety
     ///
     /// The pointer must have originated from the [`into_raw`] and must still own its potential
-    /// weak reference.
+    /// weak reference, and must point to a block of memory allocated by global allocator.
     ///
     /// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
     /// takes ownership of one weak reference currently represented as a raw pointer (the weak