diff --git a/src/math.rs b/src/math.rs
index b5b6b5a..ecf6331 100644
--- a/src/math.rs
+++ b/src/math.rs
@@ -35,7 +35,7 @@ trait Abs {
 }
 
 #[inline]
-pure fn abs<T: Abs>(x: T) -> T {
+pure fn abs<T: Abs>(x: &T) -> T {
     x.abs()
 }