diff --git a/fasta.cabal b/fasta.cabal
--- a/fasta.cabal
+++ b/fasta.cabal
@@ -10,7 +10,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.5.1.5
+version:             0.5.2.0
 
 -- A short (one-line) description of the package.
 synopsis:            A simple, mindless parser for fasta files.
@@ -65,7 +65,7 @@
   
   -- Other library packages from which modules are imported.
   build-depends:       base >=4.6 && <4.9,
-                       parsec >=3.1.0 && <4.0,
+                       parsec >=3.1 && <4.0,
                        text >=1.1.0 && <1.4,
                        containers >= 0.5 && <0.6,
                        split >= 0.2 && <0.3
diff --git a/src/Data/Fasta/String/Parse.hs b/src/Data/Fasta/String/Parse.hs
--- a/src/Data/Fasta/String/Parse.hs
+++ b/src/Data/Fasta/String/Parse.hs
@@ -82,6 +82,12 @@
   where
     noN = map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
 
+-- | Remove Ns from a sequence
+removeN :: FastaSequence -> FastaSequence
+removeN x = x { fastaSeq = noN . fastaSeq $ x }
+  where
+    noN = map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
+
 -- | Remove Ns from a collection of CLIP fasta sequences
 removeCLIPNs :: CloneMap -> CloneMap
 removeCLIPNs = M.fromList . map remove . M.toList
diff --git a/src/Data/Fasta/Text/Lazy/Parse.hs b/src/Data/Fasta/Text/Lazy/Parse.hs
--- a/src/Data/Fasta/Text/Lazy/Parse.hs
+++ b/src/Data/Fasta/Text/Lazy/Parse.hs
@@ -6,6 +6,7 @@
 -}
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE BangPatterns #-}
 
 module Data.Fasta.Text.Lazy.Parse ( parseFasta
                                   , parseCLIPFasta
@@ -15,7 +16,7 @@
 -- Built-in
 import Data.Char
 import Control.Monad (void)
-import qualified Data.Map as M
+import qualified Data.Map.Strict as M
 import Text.Parsec
 import Text.Parsec.Text.Lazy
 import qualified Data.Text.Lazy as T
@@ -71,7 +72,7 @@
 -- | Parse a CLIP fasta file into lazy text sequences
 parseCLIPFasta :: T.Text -> CloneMap
 parseCLIPFasta = M.fromList
-               . map (\(x, (y, z)) -> ((x, y), z))
+               . map (\(!x, (!y, !z)) -> ((x, y), z))
                . zip [0..]
                . eToV
                . parse fastaCLIPFile "error"
@@ -85,10 +86,16 @@
   where
     noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
 
+-- | Remove Ns from a sequence
+removeN :: FastaSequence -> FastaSequence
+removeN x = x { fastaSeq = noN . fastaSeq $ x }
+  where
+    noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
+
 -- | Remove Ns from a collection of CLIP fasta sequences
 removeCLIPNs :: CloneMap -> CloneMap
 removeCLIPNs = M.fromList . map remove . M.toList
   where
-    remove   ((x, y), z)    = ((x, newSeq y), map newSeq z)
-    newSeq x = x { fastaSeq = noN . fastaSeq $ x }
+    remove   ((!x, !y), !z)    = ((x, newSeq y), map newSeq z)
+    newSeq !x = x { fastaSeq = noN . fastaSeq $ x }
     noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
diff --git a/src/Data/Fasta/Text/Parse.hs b/src/Data/Fasta/Text/Parse.hs
--- a/src/Data/Fasta/Text/Parse.hs
+++ b/src/Data/Fasta/Text/Parse.hs
@@ -6,6 +6,7 @@
 -}
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE BangPatterns #-}
 
 module Data.Fasta.Text.Parse ( parseFasta
                              , parseCLIPFasta
@@ -14,7 +15,7 @@
 
 -- Built-in
 import Data.Char
-import qualified Data.Map as M
+import qualified Data.Map.Strict as M
 import Control.Monad (void)
 import Text.Parsec
 import Text.Parsec.Text
@@ -72,7 +73,7 @@
 -- | Parse a CLIP fasta file into text sequences
 parseCLIPFasta :: T.Text -> CloneMap
 parseCLIPFasta = M.fromList
-               . map (\(x, (y, z)) -> ((x, y), z))
+               . map (\(!x, (!y, !z)) -> ((x, y), z))
                . zip [0..]
                . eToV
                . parse fastaCLIPFile "error"
@@ -86,10 +87,16 @@
   where
     noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
 
+-- | Remove Ns from a sequence
+removeN :: FastaSequence -> FastaSequence
+removeN x = x { fastaSeq = noN . fastaSeq $ x }
+  where
+    noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')
+
 -- | Remove Ns from a collection of CLIP fasta sequences
 removeCLIPNs :: CloneMap -> CloneMap
 removeCLIPNs = M.fromList . map remove . M.toList
   where
-    remove   ((x, y), z)    = ((x, newSeq y), map newSeq z)
-    newSeq x = x { fastaSeq = noN . fastaSeq $ x }
+    remove   ((!x, !y), !z)    = ((x, newSeq y), map newSeq z)
+    newSeq !x = x { fastaSeq = noN . fastaSeq $ x }
     noN = T.map (\y -> if (y /= 'N' && y /= 'n') then y else '-')