diff --git a/src/libcollections/string.rs b/src/libcollections/string.rs
index eedf4c2c11f34..8ba5c6ffbf2eb 100644
--- a/src/libcollections/string.rs
+++ b/src/libcollections/string.rs
@@ -701,6 +701,12 @@ impl String {
     /// Violating these may cause problems like corrupting the allocator's
     /// internal datastructures.
     ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `String` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
     /// # Examples
     ///
     /// Basic usage:
diff --git a/src/libcollections/vec.rs b/src/libcollections/vec.rs
index da56b21cf0c05..3c221f0fea0df 100644
--- a/src/libcollections/vec.rs
+++ b/src/libcollections/vec.rs
@@ -342,12 +342,18 @@ impl<T> Vec<T> {
     ///
     /// * `ptr` needs to have been previously allocated via `String`/`Vec<T>`
     ///   (at least, it's highly likely to be incorrect if it wasn't).
-    /// * `length` needs to be the length that less than or equal to `capacity`.
+    /// * `length` needs to be less than or equal to `capacity`.
     /// * `capacity` needs to be the capacity that the pointer was allocated with.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal datastructures.
     ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
     /// # Examples
     ///
     /// ```