diff --git a/src/test/test_vec.rs b/src/test/test_vec.rs
index 28abb7b..eed05ba 100644
--- a/src/test/test_vec.rs
+++ b/src/test/test_vec.rs
@@ -130,7 +130,7 @@ fn test_Vec3() {
     mut_a.swap(1, 2);
     assert mut_a[1] == a[2];
     assert mut_a[2] == a[1];
-    let mut mut_a = a;
+    mut_a = a;
     
     assert a.x == 1f;
     assert a.y == 2f;
@@ -141,6 +141,10 @@ fn test_Vec3() {
     
     assert a.cross(&b) == Vec3::new(-3f, 6f, -3f);
     
+    mut_a.cross_self(&b);
+    assert mut_a == a.cross(&b);
+    mut_a = a;
+    
     assert -a      == Vec3::new(-1f, -2f, -3f);
     assert a.neg() == Vec3::new(-1f, -2f, -3f);
     
diff --git a/src/vec.rs b/src/vec.rs
index 7220180..487cd3d 100644
--- a/src/vec.rs
+++ b/src/vec.rs
@@ -143,6 +143,16 @@ pub trait NumericVector3<T>: NumericVector<T> {
     pure fn cross(&self, other: &self) -> self;
 }
 
+/**
+ * A mutable 3-dimensional vector with numeric components
+ */
+pub trait MutableNumericVector3<T>: MutableNumericVector<&self/T> {
+    /**
+     * Set to the cross product of the vector and `other`
+     */
+    fn cross_self(&mut self, other: &self);
+}
+
 /**
  * A 4-dimensional vector with numeric components
  */
@@ -525,15 +535,6 @@ pub impl<T:Copy Number> Vec3<T>: Neg<Vec3<T>> {
     }
 }
 
-pub impl<T:Copy Number> Vec3<T>: NumericVector3<T> {
-    #[inline(always)]
-    pure fn cross(&self, other: &Vec3<T>) -> Vec3<T> {
-        Vec3::new((self[1] * other[2]) - (self[2] * other[1]),
-                  (self[2] * other[0]) - (self[0] * other[2]),
-                  (self[0] * other[1]) - (self[1] * other[0]))
-    }
-}
-
 pub impl<T:Copy Number> Vec3<T>: MutableNumericVector<&self/T> {
     #[inline(always)]
     fn neg_self(&mut self) {
@@ -571,6 +572,22 @@ pub impl<T:Copy Number> Vec3<T>: MutableNumericVector<&self/T> {
     }
 }
 
+pub impl<T:Copy Number> Vec3<T>: NumericVector3<T> {
+    #[inline(always)]
+    pure fn cross(&self, other: &Vec3<T>) -> Vec3<T> {
+        Vec3::new((self[1] * other[2]) - (self[2] * other[1]),
+                  (self[2] * other[0]) - (self[0] * other[2]),
+                  (self[0] * other[1]) - (self[1] * other[0]))
+    }
+}
+
+pub impl<T:Copy Number> Vec3<T>: MutableNumericVector3<&self/T> {
+    #[inline(always)]
+    fn cross_self(&mut self, other: &Vec3<T>) {
+        *self = self.cross(other);
+    }
+}
+
 pub impl<T:Copy Number Exp> Vec3<T>: GeometricVector<T> {
     #[inline(always)]
     pure fn length2(&self) -> T {