diff --git a/src/mat2.rs b/src/mat2.rs
index 9460841..75efda0 100644
--- a/src/mat2.rs
+++ b/src/mat2.rs
@@ -220,7 +220,8 @@ impl<T:Copy + Float + FuzzyEq<T> + Add<T,T> + Sub<T,T> + Mul<T,T> + Div<T,T> + N
 
     #[inline(always)]
     fn swap_cols(&mut self, a: uint, b: uint) {
-        swap(&mut self.x, &mut self.y);
+        swap(self.col_mut(a),
+             self.col_mut(b));
     }
 
     #[inline(always)]