diff --git a/chr-core.cabal b/chr-core.cabal
--- a/chr-core.cabal
+++ b/chr-core.cabal
@@ -2,7 +2,7 @@
 -- see http://haskell.org/cabal/users-guide/
 
 name:                chr-core
-version:             0.1.0.0
+version:             0.1.0.1
 synopsis:            Constraint Handling Rules
 description:         Constraint Handling Rules evaluation engine
 license:             BSD3
@@ -40,7 +40,7 @@
     FlexibleInstances,
     RankNTypes
   build-depends:      
-    base >=4.9 && < 5,
+    base >=4.8 && < 5,
     -- array >= 0.3,
     hashable >= 1.2.4,
     unordered-containers >= 0.2.7,
diff --git a/src/CHR/Solve/MonoBacktrackPrio.hs b/src/CHR/Solve/MonoBacktrackPrio.hs
--- a/src/CHR/Solve/MonoBacktrackPrio.hs
+++ b/src/CHR/Solve/MonoBacktrackPrio.hs
@@ -1109,7 +1109,8 @@
 
 -- | Match the stored CHR with a set of possible constraints, giving a substitution on success
 slvMatch
-  :: ( MonoBacktrackPrio c g bp p s env m
+  :: forall c g bp p s env m
+   . ( MonoBacktrackPrio c g bp p s env m
      -- these below should not be necessary as they are implied (via superclasses) by MonoBacktrackPrio, but deeper nested superclasses seem not to be picked up...
      , CHRMatchable env c s
      , CHRCheckable env g s
@@ -1125,7 +1126,7 @@
        -> CHRMonoBacktrackPrioT c g bp p s env m (Maybe (FoundSlvMatch c g bp p s))
 slvMatch env chr@(StoredCHR {_storedChrRule = Rule {rulePrio = mbpr, ruleHead = hc, ruleGuard = gd, ruleBacktrackPrio = mbbpr, ruleBodyAlts = alts}}) cnstrs headInx = do
     subst <- getl $ bst ^* chrbstSolveSubst
-    curbprio <- fmap chrPrioLift $ getl $ bst ^* chrbstBacktrackPrio
+    curbprio <- fmap (chrPrioLift (Proxy :: Proxy env) (Proxy :: Proxy s)) $ getl $ bst ^* chrbstBacktrackPrio
     return $ fmap (\(s,ws) -> FoundSlvMatch s freevars ws (FoundMatchSortKey (fmap ((,) s) mbpr) (Set.size ws) (_storedChrInx chr))
                     [ FoundBodyAlt i bp a | (i,a) <- zip [0..] alts, let bp = maybe minBound (chrPrioEval env s) $ rbodyaltBacktrackPrio a
                     ])
diff --git a/src/CHR/Types/Core.hs b/src/CHR/Types/Core.hs
--- a/src/CHR/Types/Core.hs
+++ b/src/CHR/Types/Core.hs
@@ -263,7 +263,7 @@
 type family CHRPrioEvaluatableVal p :: *
 
 -- | A PrioEvaluatable participates in the reduction process to indicate the rule priority, higher prio takes precedence
-class (Ord (CHRPrioEvaluatableVal x), Bounded (CHRPrioEvaluatableVal x)) => CHRPrioEvaluatable env x subst | x -> env subst where
+class (Ord (CHRPrioEvaluatableVal x), Bounded (CHRPrioEvaluatableVal x)) => CHRPrioEvaluatable env x subst where
   -- | Reduce to a prio representation
   chrPrioEval :: env -> subst -> x -> CHRPrioEvaluatableVal x
   chrPrioEval _ _ _ = minBound
@@ -273,7 +273,7 @@
   chrPrioCompare e (s1,x1) (s2,x2) = chrPrioEval e s1 x1 `compare` chrPrioEval e s2 x2
   
   -- | Lift prio val into prio
-  chrPrioLift :: CHRPrioEvaluatableVal x -> x
+  chrPrioLift :: proxy env -> proxy subst -> CHRPrioEvaluatableVal x -> x
 
 -------------------------------------------------------------------------------------------
 --- Prio