diff --git a/beacon_chain/chain/src/maps.rs b/beacon_chain/chain/src/maps.rs
index cecd87c8d..4c737cb44 100644
--- a/beacon_chain/chain/src/maps.rs
+++ b/beacon_chain/chain/src/maps.rs
@@ -45,7 +45,7 @@ mod tests {
     use super::*;
 
     fn sac_generator(
-        shard_count: u16,
+        shard_count: u64,
         slot_count: usize,
         sac_per_slot: usize,
         committee_size: usize,
diff --git a/beacon_chain/types/src/lib.rs b/beacon_chain/types/src/lib.rs
index a4f52701a..08b871c1c 100644
--- a/beacon_chain/types/src/lib.rs
+++ b/beacon_chain/types/src/lib.rs
@@ -65,7 +65,7 @@ pub type Bitfield = boolean_bitfield::BooleanBitfield;
 pub type BitfieldError = boolean_bitfield::Error;
 
 /// Maps a (slot, shard_id) to attestation_indices.
-pub type AttesterMap = HashMap<(u64, u16), Vec<usize>>;
+pub type AttesterMap = HashMap<(u64, u64), Vec<usize>>;
 
 /// Maps a slot to a block proposer.
 pub type ProposerMap = HashMap<u64, usize>;