diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 05225e5a25b29..d65c24f7350ae 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -369,7 +369,7 @@ impl<T> VecDeque<T> {
         VecDeque::with_capacity(INITIAL_CAPACITY)
     }
 
-    /// Creates an empty `VecDeque` with space for at least `n` elements.
+    /// Creates an empty `VecDeque` with space for at least `capacity` elements.
     ///
     /// # Examples
     ///
@@ -379,10 +379,10 @@ impl<T> VecDeque<T> {
     /// let vector: VecDeque<u32> = VecDeque::with_capacity(10);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn with_capacity(n: usize) -> VecDeque<T> {
+    pub fn with_capacity(capacity: usize) -> VecDeque<T> {
         // +1 since the ringbuffer always leaves one space empty
-        let cap = cmp::max(n + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
-        assert!(cap > n, "capacity overflow");
+        let cap = cmp::max(capacity + 1, MINIMUM_CAPACITY + 1).next_power_of_two();
+        assert!(cap > capacity, "capacity overflow");
 
         VecDeque {
             tail: 0,
diff --git a/src/librustc_data_structures/bit_set.rs b/src/librustc_data_structures/bit_set.rs
index ff7964646d608..ec7ff3bd81397 100644
--- a/src/librustc_data_structures/bit_set.rs
+++ b/src/librustc_data_structures/bit_set.rs
@@ -607,8 +607,8 @@ impl<T: Idx> GrowableBitSet<T> {
         GrowableBitSet { bit_set: BitSet::new_empty(0) }
     }
 
-    pub fn with_capacity(bits: usize) -> GrowableBitSet<T> {
-        GrowableBitSet { bit_set: BitSet::new_empty(bits) }
+    pub fn with_capacity(capacity: usize) -> GrowableBitSet<T> {
+        GrowableBitSet { bit_set: BitSet::new_empty(capacity) }
     }
 
     /// Returns `true` if the set has changed.
diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index bf406bb9b0ba7..e6c8e26fa92d8 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -92,10 +92,10 @@ impl<R: Read> BufReader<R> {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn with_capacity(cap: usize, inner: R) -> BufReader<R> {
+    pub fn with_capacity(capacity: usize, inner: R) -> BufReader<R> {
         unsafe {
-            let mut buffer = Vec::with_capacity(cap);
-            buffer.set_len(cap);
+            let mut buffer = Vec::with_capacity(capacity);
+            buffer.set_len(capacity);
             inner.initializer().initialize(&mut buffer);
             BufReader {
                 inner,
@@ -477,10 +477,10 @@ impl<W: Write> BufWriter<W> {
     /// let mut buffer = BufWriter::with_capacity(100, stream);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn with_capacity(cap: usize, inner: W) -> BufWriter<W> {
+    pub fn with_capacity(capacity: usize, inner: W) -> BufWriter<W> {
         BufWriter {
             inner: Some(inner),
-            buf: Vec::with_capacity(cap),
+            buf: Vec::with_capacity(capacity),
             panicked: false,
         }
     }
@@ -851,9 +851,9 @@ impl<W: Write> LineWriter<W> {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn with_capacity(cap: usize, inner: W) -> LineWriter<W> {
+    pub fn with_capacity(capacity: usize, inner: W) -> LineWriter<W> {
         LineWriter {
-            inner: BufWriter::with_capacity(cap, inner),
+            inner: BufWriter::with_capacity(capacity, inner),
             need_flush: false,
         }
     }
diff --git a/src/libstd/sys_common/wtf8.rs b/src/libstd/sys_common/wtf8.rs
index f17020de44ec5..81e606fc16583 100644
--- a/src/libstd/sys_common/wtf8.rs
+++ b/src/libstd/sys_common/wtf8.rs
@@ -146,10 +146,10 @@ impl Wtf8Buf {
         Wtf8Buf { bytes: Vec::new() }
     }
 
-    /// Creates a new, empty WTF-8 string with pre-allocated capacity for `n` bytes.
+    /// Creates a new, empty WTF-8 string with pre-allocated capacity for `capacity` bytes.
     #[inline]
-    pub fn with_capacity(n: usize) -> Wtf8Buf {
-        Wtf8Buf { bytes: Vec::with_capacity(n) }
+    pub fn with_capacity(capacity: usize) -> Wtf8Buf {
+        Wtf8Buf { bytes: Vec::with_capacity(capacity) }
     }
 
     /// Creates a WTF-8 string from a UTF-8 `String`.