diff --git a/haskell-src/exec/Chainweb/RichList.hs b/haskell-src/exec/Chainweb/RichList.hs
index 618c118..18d6309 100644
--- a/haskell-src/exec/Chainweb/RichList.hs
+++ b/haskell-src/exec/Chainweb/RichList.hs
@@ -70,7 +70,7 @@ richList logger fp (ChainwebVersion version) = do
                 (fdl, cdl) = foldMap go files
                 chains = cdl []
                 isConsecutive = all (\(x,y) -> succ x == y)
-                  . (zip <*> tail)
+                  . (zip <*> (drop 1))
                   . sort
             unless (isConsecutive chains)
               $ ioError $ userError
diff --git a/haskell-src/lib/ChainwebData/Backfill.hs b/haskell-src/lib/ChainwebData/Backfill.hs
index 774b5e7..d849f4c 100644
--- a/haskell-src/lib/ChainwebData/Backfill.hs
+++ b/haskell-src/lib/ChainwebData/Backfill.hs
@@ -14,6 +14,7 @@ import Data.Maybe (mapMaybe)
 import Chainweb.Api.ChainId (ChainId(..))
 import ChainwebData.Genesis
 import ChainwebData.Types
+import qualified Data.List.NonEmpty as NE
 
 
 lookupPlan :: GenesisInfo -> Map ChainId Int -> [(ChainId, Low, High)]
@@ -30,7 +31,7 @@ lookupPlan gi = M.foldrWithKey go []
             -- calculate 100-entry batches using min blockheight @cmin@
             -- and genesis height
             --
-            ranges = map (Low . last &&& High . head) $
+            ranges = map (Low . NE.last &&& High . NE.head) $
               groupsOf blockRequestSize [cmin - 1, cmin - 2 .. genesis]
 
             -- calculate high water entry against minimum block height for cid
@@ -63,7 +64,7 @@ oldLookupPlan mins = concatMap (\pair -> mapMaybe (g pair) asList) ranges
     asList = map (second (\n -> High . max 0 $ n - 1)) $ M.toList mins
 
     ranges :: [(Low, High)]
-    ranges = map (Low . last &&& High . head) $ groupsOf blockRequestSize [maxi, maxi-1 .. 0]
+    ranges = map (Low . NE.last &&& High . NE.head) $ groupsOf blockRequestSize [maxi, maxi-1 .. 0]
 
     g :: (Low, High) -> (ChainId, High) -> Maybe (ChainId, Low, High)
     g (l@(Low l'), u) (cid, mx@(High mx'))
diff --git a/haskell-src/lib/ChainwebData/Types.hs b/haskell-src/lib/ChainwebData/Types.hs
index afe5085..8bc915d 100644
--- a/haskell-src/lib/ChainwebData/Types.hs
+++ b/haskell-src/lib/ChainwebData/Types.hs
@@ -35,6 +35,7 @@ import           Data.Time.Clock.POSIX (posixSecondsToUTCTime)
 import           Control.Lens
 import           Data.Aeson.Lens
 import           Network.Wai.EventSource.Streaming
+import           Data.List.NonEmpty (nonEmpty)
 
 ---
 
@@ -72,7 +73,7 @@ hashToDbHash = DbHash . hashB64U
 
 -- | Break a list into groups of @n@ elements. The last item in the result is
 -- not guaranteed to have the same length as the others.
-groupsOf :: Int -> [a] -> [[a]]
+groupsOf :: Int -> [a] -> [NonEmpty a]
 groupsOf n as
   | n <= 0 = []
   | otherwise = go as
@@ -80,7 +81,9 @@ groupsOf n as
     go [] = []
     go bs = xs : go rest
       where
-        (xs, rest) = splitAt n bs
+        -- Since n > 0, _xs is never Empty, fromJust will never throw an error
+        xs = (fromJust . nonEmpty) _xs
+        (_xs, rest) = splitAt n bs
 
 newtype Low = Low Int
   deriving newtype (Eq, Ord, Show, Num)