diff --git a/src/Datalog/Eval.hs b/src/Datalog/Eval.hs
index 9b26770..28703c0 100644
--- a/src/Datalog/Eval.hs
+++ b/src/Datalog/Eval.hs
@@ -145,10 +145,16 @@ evalConjunction db atoms = do
   return (foldr (><) (Set.singleton Map.empty) rs)
 
 projectTuple :: Set ConId -> Map VarId ConId -> [Term] -> Set [ConId]
-projectTuple univ m = Set.fromList . mapM proj
+projectTuple univ m0 ts0 = Set.fromList $ proj m0 ts0
   where
-    proj (Con c) = [c]
-    proj (Var v) = Map.findWithDefault (Set.toList univ) v (fmap (:[]) m)
+    proj _ [] = [[]]
+    proj m (Con c : ts) = map (c:) (proj m ts)
+    proj m (Var v : ts) = case Map.lookup v m of
+      Just c -> map (c:) (proj m ts)
+      Nothing -> do
+        c <- Set.toList univ
+        s <- proj (Map.insert v c m) ts
+        return (c : s)
 
 immediateConsequences :: Database -> Rule -> Either EvalError (Set [ConId])
 immediateConsequences db (Atom _ ts :- bodyAtoms) = do