diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 97b3554b1e1ba3455e3ea2cccb9bc89370d04b67..937f73a326271491145514785d04afbeda07e00f 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -88,7 +88,7 @@ pub fn align_of_val<T>(_val: &T) -> uint {
 
 /// Create a value initialized to zero.
 ///
-/// This function is similar to allocating space for a a local variable and
+/// This function is similar to allocating space for a local variable and
 /// zeroing it out (an unsafe operation).
 ///
 /// Care must be taken when using this function, if the type `T` has a
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 01c9277a20b75d79d96fddfac024a2be868e8b58..a794897ce6bc8dca662f5e6ecd88e40c6889bc17 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -198,7 +198,7 @@ fn count_zeros(self) -> uint {
     /// ```
     fn swap_bytes(self) -> Self;
 
-    /// Convert a integer from big endian to the target's endianness.
+    /// Convert an integer from big endian to the target's endianness.
     ///
     /// On big endian this is a no-op. On little endian the bytes are swapped.
     ///
@@ -220,7 +220,7 @@ fn from_be(x: Self) -> Self {
         if cfg!(target_endian = "big") { x } else { x.swap_bytes() }
     }
 
-    /// Convert a integer from little endian to the target's endianness.
+    /// Convert an integer from little endian to the target's endianness.
     ///
     /// On little endian this is a no-op. On big endian the bytes are swapped.
     ///