diff --git a/Data/Text/Template.hs b/Data/Text/Template.hs
--- a/Data/Text/Template.hs
+++ b/Data/Text/Template.hs
@@ -46,7 +46,7 @@
 
 import Control.Applicative (Applicative(pure), (<$>))
 import Control.Monad (liftM, liftM2)
-import Control.Monad.State (State, evalState, get, put)
+import Control.Monad.State.Strict (State, evalState, get, put)
 import Data.Char (isAlphaNum)
 import Data.Function (on)
 import Data.Traversable (traverse)
@@ -215,17 +215,22 @@
 -- -----------------------------------------------------------------------------
 -- Text parser
 
-type Parser = State (T.Text, Int, Int)
+-- | The parser state.
+data S = S {-# UNPACK #-} !T.Text  -- ^ Remaining input
+           {-# UNPACK #-} !Int     -- ^ Row
+           {-# UNPACK #-} !Int     -- ^ Col
 
+type Parser = State S
+
 char :: Parser (Maybe Char)
 char = do
-    (s, row, col) <- get
+    S s row col <- get
     if T.null s
       then return Nothing
       else do c <- return $! T.head s
               case c of
-                '\n' -> put (T.tail s, row + 1 :: Int, 1 :: Int)
-                _    -> put (T.tail s, row, col + 1 :: Int)
+                '\n' -> put $! S (T.tail s) (row + 1) 1
+                _    -> put $! S (T.tail s) row (col + 1)
               return $ Just c
 
 peek :: Parser (Maybe Char)
@@ -245,7 +250,7 @@
 
 takeWhile :: (Char -> Bool) -> Parser T.Text
 takeWhile p = do
-    (s, row, col) <- get
+    S s row col <- get
     case T.spanBy p s of
       (x, s') -> do
                   let xlines = T.lines x
@@ -257,16 +262,16 @@
                                _  -> T.length (last xlines)
                                      -- Selection extends
                                      -- to next line at least
-                  put (s', row', col')
+                  put $! S s' row' col'
                   return x
 
 pos :: Parser (Int, Int)
 pos = do
-    (_, row, col) <- get
+    S _ row col <- get
     return (row, col)
 
 runParser :: Parser a -> T.Text -> a
-runParser p s = evalState p (s, 1 :: Int, 1 :: Int)
+runParser p s = evalState p $ S s 1 1
 
 -- -----------------------------------------------------------------------------
 -- Example
diff --git a/template.cabal b/template.cabal
--- a/template.cabal
+++ b/template.cabal
@@ -1,5 +1,5 @@
 name:                template
-version:             0.2.0.1
+version:             0.2.0.2
 description:
   Simple string substitution library that supports \"$\"-based
   substitution.  Meant to be used when Text.Printf or string
@@ -19,8 +19,8 @@
   exposed-modules:  Data.Text.Template
 
   build-depends:
-    base < 5,
-    mtl < 1.2,
+    base >= 3.0 && < 4.4,
+    mtl >= 1.1 && < 2.0.2,
     text >= 0.7.2 && < 0.11
 
   ghc-options: -funbox-strict-fields -Wall