diff --git a/what4/src/What4/Protocol/VerilogWriter.hs b/what4/src/What4/Protocol/VerilogWriter.hs
index ae4d5ca7..00a1a12a 100644
--- a/what4/src/What4/Protocol/VerilogWriter.hs
+++ b/what4/src/What4/Protocol/VerilogWriter.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-
 Module           : What4.Protocol.VerilogWriter.AST
 Copyright        : (c) Galois, Inc 2020
diff --git a/what4/src/What4/Solver/CVC5.hs b/what4/src/What4/Solver/CVC5.hs
index 1c0d0ea8..2cc52f72 100644
--- a/what4/src/What4/Solver/CVC5.hs
+++ b/what4/src/What4/Solver/CVC5.hs
@@ -15,6 +15,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 
 module What4.Solver.CVC5
   ( CVC5(..)
diff --git a/what4/src/What4/Solver/Z3.hs b/what4/src/What4/Solver/Z3.hs
index 84db2037..0059be0f 100644
--- a/what4/src/What4/Solver/Z3.hs
+++ b/what4/src/What4/Solver/Z3.hs
@@ -14,7 +14,7 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeApplications #-}
-
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE GADTs #-}
 module What4.Solver.Z3
   ( Z3(..)
diff --git a/what4/src/What4/Utils/OnlyIntRepr.hs b/what4/src/What4/Utils/OnlyIntRepr.hs
index e995bd63..6c8dad7b 100644
--- a/what4/src/What4/Utils/OnlyIntRepr.hs
+++ b/what4/src/What4/Utils/OnlyIntRepr.hs
@@ -8,6 +8,7 @@ Defines a GADT for indicating a base type must be an integer.  Used for
 restricting index types in MATLAB arrays.
 -}
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE TypeOperators #-}
 module What4.Utils.OnlyIntRepr
   ( OnlyIntRepr(..)
   , toBaseTypeRepr
diff --git a/what4/test/InvariantSynthesis.hs b/what4/test/InvariantSynthesis.hs
index 32b995fd..fc826f68 100644
--- a/what4/test/InvariantSynthesis.hs
+++ b/what4/test/InvariantSynthesis.hs
@@ -3,6 +3,7 @@
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 
 import           ProbeSolvers
 import           Test.Tasty
diff --git a/what4/test/OnlineSolverTest.hs b/what4/test/OnlineSolverTest.hs
index e5af6e53..a7f95499 100644
--- a/what4/test/OnlineSolverTest.hs
+++ b/what4/test/OnlineSolverTest.hs
@@ -12,6 +12,7 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-} -- for TestShow instance
 
 import           Control.Concurrent ( threadDelay )