the literals are usize no u64
diff --git a/src/isaac.rs b/src/isaac.rs
index f4dd3c3..42de352 100644
--- a/src/isaac.rs
+++ b/src/isaac.rs
@@ -131,7 +131,7 @@
         const MIDPOINT: usize = RAND_SIZE_USIZE / 2;
 
         macro_rules! ind {
-            ($x:expr) => ( self.mem[($x >> 2u64).0 as usize & (RAND_SIZE_USIZE - 1)] )
+            ($x:expr) => ( self.mem[($x >> 2usize).0 as usize & (RAND_SIZE_USIZE - 1)] )
         }
 
         let r = [(0, MIDPOINT), (MIDPOINT, 0)];
@@ -370,7 +370,7 @@
         const MP_VEC: [(usize, usize); 2] = [(0,MIDPOINT), (MIDPOINT, 0)];
         macro_rules! ind {
             ($x:expr) => {
-                *self.mem.get_unchecked((($x >> 3u64).0 as usize) & (RAND_SIZE_64 - 1))
+                *self.mem.get_unchecked((($x >> 3usize).0 as usize) & (RAND_SIZE_64 - 1))
             }
         }