diff --git a/beacon_chain/validator_shuffling/src/lib.rs b/beacon_chain/validator_shuffling/src/lib.rs
index a11483e56..ee6f5e8fb 100644
--- a/beacon_chain/validator_shuffling/src/lib.rs
+++ b/beacon_chain/validator_shuffling/src/lib.rs
@@ -5,4 +5,7 @@ extern crate types;
 mod active_validator_indices;
 mod shuffle;
 
-pub use shuffle::shard_and_committees_for_cycle;
+pub use shuffle::{
+    shard_and_committees_for_cycle,
+    ValidatorAssignmentError,
+};
diff --git a/beacon_chain/validator_shuffling/src/shuffle.rs b/beacon_chain/validator_shuffling/src/shuffle.rs
index 1ce778a6b..4768c1cb1 100644
--- a/beacon_chain/validator_shuffling/src/shuffle.rs
+++ b/beacon_chain/validator_shuffling/src/shuffle.rs
@@ -1,7 +1,10 @@
 use std::cmp::min;
 
 use honey_badger_split::SplitExt;
-use vec_shuffle::shuffle;
+use vec_shuffle::{
+    shuffle,
+    ShuffleErr,
+};
 use types::{
     ShardAndCommittee,
     ValidatorRecord,
@@ -12,12 +15,12 @@ use super::active_validator_indices::active_validator_indices;
 
 type DelegatedCycle = Vec<Vec<ShardAndCommittee>>;
 
-#[derive(Debug)]
-pub enum TransitionError {
-	InvalidInput(String),
+#[derive(Debug, PartialEq)]
+pub enum ValidatorAssignmentError {
+    TooManyValidators,
+    TooFewShards,
 }
 
-
 /// Delegates active validators into slots for a given cycle, given a random seed.
 /// Returns a vector or ShardAndComitte vectors representing the shards and committiees for
 /// each slot.
@@ -27,15 +30,11 @@ pub fn shard_and_committees_for_cycle(
     validators: &[ValidatorRecord],
     crosslinking_shard_start: u16,
     config: &ChainConfig)
-    -> Result<DelegatedCycle, TransitionError>
+    -> Result<DelegatedCycle, ValidatorAssignmentError>
 {
     let shuffled_validator_indices = {
         let mut validator_indices = active_validator_indices(validators);
-        match shuffle(seed, validator_indices) {
-            Ok(shuffled) => shuffled,
-            _ => return Err(TransitionError::InvalidInput(
-                    String::from("Shuffle list length exceed.")))
-        }
+        shuffle(seed, validator_indices)?
     };
     let shard_indices: Vec<usize> = (0_usize..config.shard_count as usize).into_iter().collect();
     let crosslinking_shard_start = crosslinking_shard_start as usize;
@@ -56,17 +55,14 @@ fn generate_cycle(
     crosslinking_shard_start: usize,
     cycle_length: usize,
     min_committee_size: usize)
-    -> Result<DelegatedCycle, TransitionError>
+    -> Result<DelegatedCycle, ValidatorAssignmentError>
 {
 
     let validator_count = validator_indices.len();
     let shard_count = shard_indices.len();
 
     if shard_count / cycle_length == 0 {
-	    return Err(TransitionError::InvalidInput(String::from("Number of
-					    shards needs to be greater than
-					    cycle length")));
-
+        return Err(ValidatorAssignmentError::TooFewShards)
     }
 
     let (committees_per_slot, slots_per_committee) = {
@@ -105,6 +101,14 @@ fn generate_cycle(
     Ok(cycle)
 }
 
+impl From<ShuffleErr> for ValidatorAssignmentError {
+    fn from(e: ShuffleErr) -> ValidatorAssignmentError {
+        match e {
+            ShuffleErr::ExceedsListLength => ValidatorAssignmentError::TooManyValidators,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -115,7 +119,7 @@ mod tests {
         crosslinking_shard_start: usize,
         cycle_length: usize,
         min_committee_size: usize)
-        -> (Vec<usize>, Vec<usize>, Result<DelegatedCycle, TransitionError>)
+        -> (Vec<usize>, Vec<usize>, Result<DelegatedCycle, ValidatorAssignmentError>)
     {
         let validator_indices: Vec<usize> = (0_usize..*validator_count).into_iter().collect();
         let shard_indices: Vec<usize> = (0_usize..*shard_count).into_iter().collect();