diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,7 @@
+0.9.1.7:
+
+  Turns out one of the constraints is needed by GHC 7.6.
+
 0.9.1.6:
 
   Updated dependencies to support GHC 8.0 (RC1) and updated the code to
diff --git a/src/Swish/VarBinding.hs b/src/Swish/VarBinding.hs
--- a/src/Swish/VarBinding.hs
+++ b/src/Swish/VarBinding.hs
@@ -114,8 +114,8 @@
 
 -- |Return a list of the variables bound by a supplied variable binding
 --
-boundVars :: Ord a => VarBinding a b -> S.Set a
-boundVars = S.map fst . vbEnum
+boundVars :: (Ord a, Ord b) => VarBinding a b -> S.Set a
+boundVars = S.map fst . vbEnum  -- Ord b is needed got GHC 7.6
 
 -- |VarBinding subset function, tests to see if one query binding
 --  is a subset of another;  i.e. every query variable mapping defined
diff --git a/swish.cabal b/swish.cabal
--- a/swish.cabal
+++ b/swish.cabal
@@ -1,5 +1,5 @@
 Name:               swish
-Version:            0.9.1.6
+Version:            0.9.1.7
 Stability:          experimental
 License:            LGPL
 License-file:       LICENSE