diff --git a/src/length.rs b/src/length.rs
index a782846..ddda5d1 100644
--- a/src/length.rs
+++ b/src/length.rs
@@ -14,7 +14,7 @@ use num::Zero;
 use num_lib::NumCast;
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use std::cmp::Ordering;
-use std::ops::{Add, Sub, Mul, Div, Neg};
+use std::ops::{Add, AddAssign, Sub, SubAssign, Mul, Div, Neg};
 use std::marker::PhantomData;
 
 /// A one-dimensional distance, with value represented by `T` and unit of measurement `Unit`.
@@ -67,6 +67,13 @@ impl<U, T: Clone + Add<T, Output=T>> Add for Length<U, T> {
     }
 }
 
+// length += length
+impl<U, T: Clone + AddAssign<T>> AddAssign for Length<U, T> {
+    fn add_assign(&mut self, other: Length<U, T>) {
+        self.0 += other.get();
+    }
+}
+
 // length - length
 impl<U, T: Clone + Sub<T, Output=T>> Sub<Length<U, T>> for Length<U, T> {
     type Output = Length<U, T>;
@@ -75,6 +82,13 @@ impl<U, T: Clone + Sub<T, Output=T>> Sub<Length<U, T>> for Length<U, T> {
     }
 }
 
+// length -= length
+impl<U, T: Clone + SubAssign<T>> SubAssign for Length<U, T> {
+    fn sub_assign(&mut self, other: Length<U, T>) {
+        self.0 -= other.get();
+    }
+}
+
 // length / length
 impl<Src, Dst, T: Clone + Div<T, Output=T>> Div<Length<Src, T>> for Length<Dst, T> {
     type Output = ScaleFactor<Src, Dst, T>;
@@ -205,4 +219,24 @@ mod tests {
         let negative_zero_feet = -zero_feet;
         assert_eq!(negative_zero_feet.get(), 0.0);
     }
+
+    #[test]
+    fn test_addassign() {
+        let one_cm: Length<Mm, f32> = Length::new(10.0);
+        let mut measurement: Length<Mm, f32> = Length::new(5.0);
+
+        measurement += one_cm;
+
+        assert_eq!(measurement.get(), 15.0);
+    }
+
+    #[test]
+    fn test_subassign() {
+        let one_cm: Length<Mm, f32> = Length::new(10.0);
+        let mut measurement: Length<Mm, f32> = Length::new(5.0);
+
+        measurement -= one_cm;
+
+        assert_eq!(measurement.get(), -5.0);
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 41a3b5e..d15a24c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -8,6 +8,8 @@
 // except according to those terms.
 
 #![feature(asm, custom_derive, plugin, repr_simd, zero_one, test)]
+#![feature(augmented_assignments)]
+#![feature(op_assign_traits)]
 
 #![plugin(serde_macros)]