diff --git a/src/collections/binary_heap/extend.rs b/src/collections/binary_heap/extend.rs
index 8538f9b..4503fe3 100644
--- a/src/collections/binary_heap/extend.rs
+++ b/src/collections/binary_heap/extend.rs
@@ -10,9 +10,9 @@ impl<T: Ord> Extend<T> for BinaryHeap<T> {
         stream: S,
     ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
         let stream = stream.into_stream();
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let (lower_bound, _) = stream.size_hint();
-        //self.reserve(lower_bound);
+
+        self.reserve(stream.size_hint().0);
+
         Box::pin(stream.for_each(move |item| self.push(item)))
     }
 }
diff --git a/src/collections/hash_map/extend.rs b/src/collections/hash_map/extend.rs
index 5f96b8a..c34bb9e 100644
--- a/src/collections/hash_map/extend.rs
+++ b/src/collections/hash_map/extend.rs
@@ -23,13 +23,12 @@ where
         // hint lower bound if the map is empty. Otherwise reserve half the hint (rounded up), so
         // the map will only resize twice in the worst case.
 
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let reserve = if self.is_empty() {
-        //    stream.size_hint().0
-        //} else {
-        //    (stream.size_hint().0 + 1) / 2
-        //};
-        //self.reserve(reserve);
+        let additional = if self.is_empty() {
+            stream.size_hint().0
+        } else {
+            (stream.size_hint().0 + 1) / 2
+        };
+        self.reserve(additional);
 
         Box::pin(stream.for_each(move |(k, v)| {
             self.insert(k, v);
diff --git a/src/collections/hash_set/extend.rs b/src/collections/hash_set/extend.rs
index 72400e1..123e844 100644
--- a/src/collections/hash_set/extend.rs
+++ b/src/collections/hash_set/extend.rs
@@ -26,13 +26,12 @@ where
         // hint lower bound if the map is empty. Otherwise reserve half the hint (rounded up), so
         // the map will only resize twice in the worst case.
 
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let reserve = if self.is_empty() {
-        //    stream.size_hint().0
-        //} else {
-        //    (stream.size_hint().0 + 1) / 2
-        //};
-        //self.reserve(reserve);
+        let additional = if self.is_empty() {
+            stream.size_hint().0
+        } else {
+            (stream.size_hint().0 + 1) / 2
+        };
+        self.reserve(additional);
 
         Box::pin(stream.for_each(move |item| {
             self.insert(item);
diff --git a/src/collections/linked_list/extend.rs b/src/collections/linked_list/extend.rs
index 567a92d..63a1a97 100644
--- a/src/collections/linked_list/extend.rs
+++ b/src/collections/linked_list/extend.rs
@@ -10,9 +10,6 @@ impl<T> Extend<T> for LinkedList<T> {
         stream: S,
     ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
         let stream = stream.into_stream();
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let (lower_bound, _) = stream.size_hint();
-        //self.reserve(lower_bound);
         Box::pin(stream.for_each(move |item| self.push_back(item)))
     }
 }
diff --git a/src/collections/vec_deque/extend.rs b/src/collections/vec_deque/extend.rs
index d034bdc..17e396a 100644
--- a/src/collections/vec_deque/extend.rs
+++ b/src/collections/vec_deque/extend.rs
@@ -10,9 +10,9 @@ impl<T> Extend<T> for VecDeque<T> {
         stream: S,
     ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
         let stream = stream.into_stream();
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let (lower_bound, _) = stream.size_hint();
-        //self.reserve(lower_bound);
+
+        self.reserve(stream.size_hint().0);
+
         Box::pin(stream.for_each(move |item| self.push_back(item)))
     }
 }
diff --git a/src/string/extend.rs b/src/string/extend.rs
index 72260a5..8572cc3 100644
--- a/src/string/extend.rs
+++ b/src/string/extend.rs
@@ -10,9 +10,8 @@ impl Extend<char> for String {
         stream: S,
     ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
         let stream = stream.into_stream();
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        // let (lower_bound, _) = stream.size_hint();
-        // self.reserve(lower_bound);
+
+        self.reserve(stream.size_hint().0);
 
         Box::pin(stream.for_each(move |c| self.push(c)))
     }
diff --git a/src/vec/extend.rs b/src/vec/extend.rs
index ca3373d..ecf68c8 100644
--- a/src/vec/extend.rs
+++ b/src/vec/extend.rs
@@ -9,9 +9,9 @@ impl<T> Extend<T> for Vec<T> {
         stream: S,
     ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
         let stream = stream.into_stream();
-        //TODO: Add this back in when size_hint is added to Stream/StreamExt
-        //let (lower_bound, _) = stream.size_hint();
-        //self.reserve(lower_bound);
+
+        self.reserve(stream.size_hint().0);
+
         Box::pin(stream.for_each(move |item| self.push(item)))
     }
 }