diff --git a/src/lib.rs b/src/lib.rs
index a9ff6f0..f3f8ceb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -501,13 +501,11 @@ impl GetSize for std::path::PathBuf {
 
 impl GetSize for &std::path::Path {}
 
-impl<T> GetSize for Box<[T]> {
+impl<T> GetSize for Box<[T]>
+where
+    T: GetSize,
+{
     fn get_heap_size(&self) -> usize {
-        let mut total = 0;
-        for item in self.iter() {
-            total += item.get_size()
-        }
-
-        total
+        self.iter().map(GetSize::get_size).sum()
     }
 }
diff --git a/tests/mod.rs b/tests/mod.rs
index 5bd5609..c161317 100644
--- a/tests/mod.rs
+++ b/tests/mod.rs
@@ -246,3 +246,16 @@ fn derive_newtype() {
     let test = TestNewType(0);
     assert_eq!(u64::get_stack_size(), test.get_size());
 }
+
+#[test]
+fn boxed_slice() {
+    use std::mem::size_of;
+    let boxed = vec![1u8; 10].into_boxed_slice();
+    assert_eq!(boxed.get_heap_size(), size_of::<u8>() * boxed.len());
+
+    let boxed = vec![1u32; 10].into_boxed_slice();
+    assert_eq!(boxed.get_heap_size(), size_of::<u32>() * boxed.len());
+
+    let boxed = vec![&1u8; 10].into_boxed_slice();
+    assert_eq!(boxed.get_heap_size(), size_of::<&u8>() * boxed.len());
+}