diff --git a/src/runtime/haskell/PGF/Forest.hs b/src/runtime/haskell/PGF/Forest.hs
index 4c59ce0d9..4cc3dd908 100644
--- a/src/runtime/haskell/PGF/Forest.hs
+++ b/src/runtime/haskell/PGF/Forest.hs
@@ -12,7 +12,7 @@
 -------------------------------------------------
 
 module PGF.Forest( Forest(..)
-                 , BracketedString, showBracketedString
+                 , BracketedString, showBracketedString, lengthBracketedString
                  , linearizeWithBrackets
                  ) where
 
diff --git a/src/runtime/haskell/PGF/Macros.hs b/src/runtime/haskell/PGF/Macros.hs
index 0670a0d20..f4bfae646 100644
--- a/src/runtime/haskell/PGF/Macros.hs
+++ b/src/runtime/haskell/PGF/Macros.hs
@@ -240,6 +240,11 @@ showBracketedString = render . ppBracketedString
 ppBracketedString (Leaf t) = text t
 ppBracketedString (Bracket cat fcat index bss) = parens (ppCId cat <+> hsep (map ppBracketedString bss))
 
+-- | The length of the bracketed string in number of tokens.
+lengthBracketedString :: BracketedString -> Int
+lengthBracketedString (Leaf _)            = 1
+lengthBracketedString (Bracket _ _ _ bss) = sum (map lengthBracketedString bss)
+
 untokn :: String -> BracketedTokn -> (String,[BracketedString])
 untokn nw (LeafKS ts)   = (head ts,map Leaf ts)
 untokn nw (LeafKP d vs) = let ts = sel d vs nw