diff --git a/System/Dzen/Bars.hs b/System/Dzen/Bars.hs
--- a/System/Dzen/Bars.hs
+++ b/System/Dzen/Bars.hs
@@ -52,7 +52,7 @@
 maybeLeft True  = AtLeft Percentage
 
 -- | Mimics the dbar utility. Uses the 'dbar_style'.
-dbar :: (Num a, Enum a, Ord a)
+dbar :: (Num a, Enum a, Ord a, Show a)
      => Bool  -- ^ If @True@, write the percentage on the left.
      -> Width -- ^ Width of the bar interior.
      -> (a,a) -- ^ Minimum and maximum values.
@@ -61,7 +61,7 @@
 dbar p = bar (maybeLeft p) . dbar_style '='
 
 -- | Mimics the dbar utility while getting the input dinamically.
-cdbar :: (Num a, Enum a, Ord a) => Bool -> Width -> (a,a) -> Printer a
+cdbar :: (Num a, Enum a, Ord a, Show a) => Bool -> Width -> (a,a) -> Printer a
 cdbar p = cbar (maybeLeft p) . dbar_style '='
 
 -- | The style produced by the dbar utility.
@@ -74,7 +74,7 @@
                       ,txtWidth      = w}
 
 -- | Mimics the gdbar utility. Uses the 'gdbar_style'.
-gdbar :: (Num a, Enum a, Ord a)
+gdbar :: (Num a, Enum a, Ord a, Show a)
       => Bool            -- ^ If @True@, write the percentage on the left.
       -> (Width, Height) -- ^ Size of the whole bar (excluding text).
       -> Maybe DColour   -- ^ Filled colour (see 'grpFilled').
@@ -87,7 +87,7 @@
 gdbar p = (((bar (maybeLeft p) .) . ) .) . gdbar_style
 
 -- | Mimics the gdbar utility while getting the input dinamically.
-cgdbar :: (Num a, Enum a, Ord a) => Bool -> (Width, Height)
+cgdbar :: (Num a, Enum a, Ord a, Show a) => Bool -> (Width, Height)
        -> Maybe DColour -> Maybe DColour -> Bool -> (a,a) -> Printer a
 cgdbar p = (((cbar (maybeLeft p) .) . ) .) . gdbar_style
 
@@ -195,7 +195,7 @@
 --   > "[                    ] 2%  "
 --
 --   so the padding always inserts the spaces on the outside.
-bar :: (Num a, Enum a, Ord a) => BarText ->
+bar :: (Num a, Enum a, Ord a, Show a) => BarText ->
        BarType -> (a,a) -> a -> DString
 bar txt bar_ r v =
     case txt of
@@ -206,13 +206,13 @@
 
 -- | 'bar' wrapped with 'simple' so that the value is
 --   taken from an input.
-cbar :: (Num a, Enum a, Ord a) => BarText ->
+cbar :: (Num a, Enum a, Ord a, Show a) => BarText ->
          BarType -> (a,a) -> Printer a
 cbar = ((simple .) .) . bar
 
 
 -- | Draws the text part of the bar.
-barText :: (Num a, Enum a, Ord a) => BarTextType -> (a,a) -> a -> DString
+barText :: (Num a, Enum a, Ord a, Show a) => BarTextType -> (a,a) -> a -> DString
 barText Absolute   _     val = str $ show val
 barText Percentage range val
     = str $ (show . fst . fst $ barRound 100 range val) ++ "%"
@@ -220,7 +220,7 @@
 
 
 -- | Draws the bar itself.
-barDraw :: (Num a, Enum a, Ord a) => BarType -> (a,a) -> a -> DString
+barDraw :: (Num a, Enum a, Ord a, Show a) => BarType -> (a,a) -> a -> DString
 barDraw (Text {txtOpen = to
               ,txtFilled = tf
               ,txtMiddle = Just tm   -- <<<<<<<<
@@ -280,11 +280,11 @@
 --   Values outside the range are clamped. The boolean returned
 --   is @True@ iff the value would be one more if we rounded
 --   half-up.
-barRound :: (Num a, Enum a, Ord a) =>
+barRound :: (Num a, Enum a, Ord a, Show a) =>
             Width -> (a,a) -> a -> ((Int, Int), Bool)
 barRound w r n = let (f, b) = barRound' w r n in ((f, w - f), b)
 
-barRound' :: (Num a, Enum a, Ord a) =>
+barRound' :: (Num a, Enum a, Ord a, Show a) =>
              Width -> (a,a) -> a -> (Int, Bool)
 barRound' w (mini,maxi) n
     | maxi < mini = error "System.Dzen.Bars.bar: max value is less than min."
diff --git a/dzen-utils.cabal b/dzen-utils.cabal
--- a/dzen-utils.cabal
+++ b/dzen-utils.cabal
@@ -1,6 +1,6 @@
 cabal-version:       >= 1.2.3
 name:                dzen-utils
-version:             0.1
+version:             0.1.1
 synopsis:            Utilities for creating inputs for dzen.
 category:            System
 license:             GPL
@@ -22,7 +22,9 @@
   toplevel module "System.Dzen".
 
 library
-  build-depends:     base >= 4, colour >= 2.2, process >= 1.0
+  build-depends:     base    >= 4   && < 5
+                   , colour  >= 2.2 && < 3
+                   , process >= 1.0 && < 2
   ghc-options:       -Wall
   extensions:
     MultiParamTypeClasses,