diff --git a/src/allocator.rs b/src/allocator.rs
index 9ce4a887..11ebeb52 100644
--- a/src/allocator.rs
+++ b/src/allocator.rs
@@ -74,11 +74,9 @@ impl<A> Locked<A> {
     }
 }
 
+/// Align the given address `addr` upwards to alignment `align`.
+///
+/// Requires that `align` is a power of two.
 fn align_up(addr: usize, align: usize) -> usize {
-    let remainder = addr % align;
-    if remainder == 0 {
-        addr // addr already aligned
-    } else {
-        addr - remainder + align
-    }
+    (addr + align - 1) & !(align - 1)
 }