diff --git a/src/lib.rs b/src/lib.rs
index a761b53..7dbb2c2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,9 +14,7 @@ use std::marker::PhantomData;
 use std::mem::{size_of, align_of};
 use std::net::{Ipv4Addr, Ipv6Addr};
 use std::os::raw::c_void;
-use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, AtomicIsize, AtomicUsize};
-use std::rc::Rc;
 
 /// Get the size of a heap block.
 ///
@@ -206,12 +204,6 @@ impl<T1, T2, T3, T4, T5> HeapSizeOf for (T1, T2, T3, T4, T5)
   }
 }
 
-impl<T: HeapSizeOf> HeapSizeOf for Arc<T> {
-    fn heap_size_of_children(&self) -> usize {
-        (**self).heap_size_of_children()
-    }
-}
-
 impl<T: HeapSizeOf> HeapSizeOf for RefCell<T> {
     fn heap_size_of_children(&self) -> usize {
         self.borrow().heap_size_of_children()
@@ -241,16 +233,6 @@ impl<T: HeapSizeOf> HeapSizeOf for VecDeque<T> {
     }
 }
 
-impl<T> HeapSizeOf for Vec<Rc<T>> {
-    fn heap_size_of_children(&self) -> usize {
-        // The fate of measuring Rc<T> is still undecided, but we still want to measure
-        // the space used for storing them.
-        unsafe {
-            heap_size_of(self.as_ptr())
-        }
-    }
-}
-
 impl<T: HeapSizeOf, S> HeapSizeOf for HashSet<T, S>
     where T: Eq + Hash, S: BuildHasher {
     fn heap_size_of_children(&self) -> usize {