diff --git a/layout.cabal b/layout.cabal
--- a/layout.cabal
+++ b/layout.cabal
@@ -1,5 +1,5 @@
 Name:           layout
-Version:        0.0.0.1
+Version:        0.0.0.2
 License:        BSD3
 Author:         Robert Hensing
 Maintainer:     hackage@roberthensing.nl
diff --git a/src/Text/Layout/DisplayText.hs b/src/Text/Layout/DisplayText.hs
--- a/src/Text/Layout/DisplayText.hs
+++ b/src/Text/Layout/DisplayText.hs
@@ -75,9 +75,9 @@
 
 -- for x, x' of types a, b, or c, we assume show x == show x' <==> x == x'
 asciiTable :: --(Show a, Eq a, Show b, Eq b, Show c, Eq c)
-  ( Convertible a DisplayText
-  , Convertible b DisplayText
-  , Convertible c DisplayText ) => 
+  ( Layout a DisplayText
+  , Layout b DisplayText
+  , Layout c DisplayText ) =>
   String -> (String, String) -> [((a,b), c)] -> String
 asciiTable title (astr, bstr) table' = "Table: " ++ title ++ "\n"
                                   ++ thead ++ "\n" ++ tbody