diff --git a/src/liballoc/collections/binary_heap.rs b/src/liballoc/collections/binary_heap.rs
index fcadcb544c431..70262361211b9 100644
--- a/src/liballoc/collections/binary_heap.rs
+++ b/src/liballoc/collections/binary_heap.rs
@@ -721,6 +721,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// assert_eq!(heap.len(), 2);
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.data.len()
@@ -744,6 +745,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// assert!(!heap.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index 49e488702b4b9..a0aabbfe8bcd5 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -2074,6 +2074,7 @@ impl<K, V> BTreeMap<K, V> {
     /// a.insert(1, "a");
     /// assert_eq!(a.len(), 1);
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.length
@@ -2093,6 +2094,7 @@ impl<K, V> BTreeMap<K, V> {
     /// a.insert(1, "a");
     /// assert!(!a.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
diff --git a/src/liballoc/collections/btree/set.rs b/src/liballoc/collections/btree/set.rs
index af9a7074e4a4f..7540e4600548c 100644
--- a/src/liballoc/collections/btree/set.rs
+++ b/src/liballoc/collections/btree/set.rs
@@ -729,6 +729,7 @@ impl<T> BTreeSet<T> {
     /// v.insert(1);
     /// assert_eq!(v.len(), 1);
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.map.len()
@@ -746,6 +747,7 @@ impl<T> BTreeSet<T> {
     /// v.insert(1);
     /// assert!(!v.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index cbf104a8fcde9..651a059dfa193 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -932,6 +932,7 @@ impl<T> VecDeque<T> {
     /// v.push_front(1);
     /// assert!(!v.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.tail == self.head
diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index f7a0bbdceafc9..88b7aa827e378 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -1180,6 +1180,7 @@ impl<T> Vec<T> {
     /// v.push(1);
     /// assert!(!v.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.len() == 0
diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 349aa029ba8cb..03d4137486ebb 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -1215,6 +1215,7 @@ impl<K, V, S> HashMap<K, V, S>
     /// a.insert(1, "a");
     /// assert_eq!(a.len(), 1);
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.table.size()
diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index 5ac3e8f9cf7d3..1de3dc5b8f394 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -461,6 +461,7 @@ impl<T, S> HashSet<T, S>
     /// v.insert(1);
     /// assert_eq!(v.len(), 1);
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn len(&self) -> usize {
         self.map.len()
@@ -478,6 +479,7 @@ impl<T, S> HashSet<T, S>
     /// v.insert(1);
     /// assert!(!v.is_empty());
     /// ```
+    #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_empty(&self) -> bool {
         self.map.is_empty()
diff --git a/src/libstd/collections/hash/table.rs b/src/libstd/collections/hash/table.rs
index 479e6dccb90dd..c40caee93b1dd 100644
--- a/src/libstd/collections/hash/table.rs
+++ b/src/libstd/collections/hash/table.rs
@@ -776,6 +776,7 @@ impl<K, V> RawTable<K, V> {
 
     /// The number of elements ever `put` in the hashtable, minus the number
     /// of elements ever `take`n.
+    #[inline]
     pub fn size(&self) -> usize {
         self.size
     }