diff --git a/src/accumulator/util.rs b/src/accumulator/util.rs
index a3d025b..4848248 100644
--- a/src/accumulator/util.rs
+++ b/src/accumulator/util.rs
@@ -233,7 +233,7 @@ pub fn parent_many(pos: u64, rise: u8, forest_rows: u8) -> Result<u64, String> {
             rise, forest_rows
         ));
     }
-    let mask = ((2 << forest_rows) - 1) as u64;
+    let mask = ((2_u64 << forest_rows) - 1) as u64;
     Ok((pos >> rise | (mask << (forest_rows - (rise - 1)) as u64)) & mask)
 }