3 files changed, 10 insertions, 1 deletions
diff --git a/compiler/GHC/Tc/Solver/Canonical.hs b/compiler/GHC/Tc/Solver/Canonical.hs
index fd608c3314..ce8bf24632 100644
--- a/compiler/GHC/Tc/Solver/Canonical.hs
+++ b/compiler/GHC/Tc/Solver/Canonical.hs
@@ -956,6 +956,11 @@ can_eq_nc'
    -> Type -> Type    -- RHS, after and before type-synonym expansion, resp
    -> TcS (StopOrContinue Ct)
 
+-- See Note [Comparing nullary type synonyms] in GHC.Core.Type.
+can_eq_nc' _flat _rdr_env _envs ev eq_rel ty1@(TyConApp tc1 []) _ps_ty1 (TyConApp tc2 []) _ps_ty2
+  | tc1 == tc2
+  = canEqReflexive ev eq_rel ty1
+
 -- Expand synonyms first; see Note [Type synonyms and canonicalization]
 can_eq_nc' rewritten rdr_env envs ev eq_rel ty1 ps_ty1 ty2 ps_ty2
   | Just ty1' <- tcView ty1 = can_eq_nc' rewritten rdr_env envs ev eq_rel ty1' ps_ty1 ty2  ps_ty2
diff --git a/compiler/GHC/Tc/Utils/TcMType.hs b/compiler/GHC/Tc/Utils/TcMType.hs
index ccb9152e01..e688dd5685 100644
--- a/compiler/GHC/Tc/Utils/TcMType.hs
+++ b/compiler/GHC/Tc/Utils/TcMType.hs
@@ -120,7 +120,6 @@ import GHC.Types.Id as Id
 import GHC.Types.Name
 import GHC.Types.Var.Set
 import GHC.Builtin.Types
-import GHC.Builtin.Types.Prim
 import GHC.Types.Var.Env
 import GHC.Types.Name.Env
 import GHC.Utils.Misc
diff --git a/compiler/GHC/Tc/Utils/TcType.hs b/compiler/GHC/Tc/Utils/TcType.hs
index 3e52419772..6e4eea8f19 100644
--- a/compiler/GHC/Tc/Utils/TcType.hs
+++ b/compiler/GHC/Tc/Utils/TcType.hs
@@ -1581,6 +1581,11 @@ tc_eq_type keep_syns vis_only orig_ty1 orig_ty2
   = go orig_env orig_ty1 orig_ty2
   where
     go :: RnEnv2 -> Type -> Type -> Bool
+    -- See Note [Comparing nullary type synonyms] in GHC.Core.Type.
+    go _   (TyConApp tc1 []) (TyConApp tc2 [])
+      | tc1 == tc2
+      = True
+
     go env t1 t2 | not keep_syns, Just t1' <- tcView t1 = go env t1' t2
     go env t1 t2 | not keep_syns, Just t2' <- tcView t2 = go env t1 t2'