diff --git a/src/runtime/haskell/PGF/Linearize.hs b/src/runtime/haskell/PGF/Linearize.hs
index 79da0e823..84b1b116f 100644
--- a/src/runtime/haskell/PGF/Linearize.hs
+++ b/src/runtime/haskell/PGF/Linearize.hs
@@ -63,7 +63,7 @@ type CncType = (CId, FId)    -- concrete type is the abstract type (the category
 
 linTree :: PGF -> Language -> Expr -> [Array LIndex BracketedTokn]
 linTree pgf lang e = 
-  [amapWithIndex (\label -> Bracket_ cat fid label [e]) lin | (_,((cat,fid),e,lin)) <- lin0 [] [] Nothing 0 e e]
+  nub [amapWithIndex (\label -> Bracket_ cat fid label [e]) lin | (_,((cat,fid),e,lin)) <- lin0 [] [] Nothing 0 e e]
   where
     cnc   = lookMap (error "no lang") lang (concretes pgf)
     lp    = lproductions cnc
diff --git a/src/runtime/haskell/PGF/Macros.hs b/src/runtime/haskell/PGF/Macros.hs
index 328bf369d..dea535af7 100644
--- a/src/runtime/haskell/PGF/Macros.hs
+++ b/src/runtime/haskell/PGF/Macros.hs
@@ -229,6 +229,7 @@ data BracketedTokn
   = LeafKS [String]
   | LeafKP [String] [Alternative]
   | Bracket_ CId {-# UNPACK #-} !FId {-# UNPACK #-} !LIndex [Expr] [BracketedTokn]    -- Invariant: the list is not empty
+  deriving Eq
 
 type LinTable = Array.Array LIndex [BracketedTokn]