diff --git a/flap/src/hopix/hopixAST.ml b/flap/src/hopix/hopixAST.ml
index d3df029..9129e63 100644
--- a/flap/src/hopix/hopixAST.ml
+++ b/flap/src/hopix/hopixAST.ml
@@ -110,7 +110,7 @@ and branch =
   | Branch of pattern located * expression located
 
 and ty =
-  (** An instantiated type constructor [t <ty₁, .., tyₙ>]. *)
+  (** An instantiated type constructor [t <ty₁, ..., tyₙ>]. *)
   | TyCon of type_constructor * ty located list
   (** A function type [ty₁ → ty₂]. *)
   | TyArrow of ty located * ty located
diff --git a/flap/src/hopix/hopixPrettyPrinter.ml b/flap/src/hopix/hopixPrettyPrinter.ml
index 93b9ebe..d59c79a 100644
--- a/flap/src/hopix/hopixPrettyPrinter.ml
+++ b/flap/src/hopix/hopixPrettyPrinter.ml
@@ -32,11 +32,12 @@ let rec program p =
 
 and definition = function
   | DefineType (t, ts, tdef) ->
+    let eq = match tdef with Abstract -> empty | _ -> string "=" in
     nest 2 (
       group (group (string "type"
                     ++ located type_constructor t
                     ^^ group (type_parameters_angles ts))
-             ++ string "=")
+             ++ eq)
       ++ type_definition tdef)
   | DeclareExtern (x, t) ->
     group (string "extern" ++ located identifier x
diff --git a/flap/src/hopix/hopixTypes.mli b/flap/src/hopix/hopixTypes.mli
index e023f3a..981d471 100644
--- a/flap/src/hopix/hopixTypes.mli
+++ b/flap/src/hopix/hopixTypes.mli
@@ -2,11 +2,8 @@ open HopixAST
 
 (** Abstract syntax for types.
 
-    The following internal syntax for types is the same as the one for
-    the types [ty] defined in {!HopixAST} except that all positions
-    have been erased.
-
- *)
+    The following internal syntax for types is the same as the one for the types
+    [ty] defined in {!HopixAST} except that all positions have been erased. *)
 type aty =
   | ATyVar   of type_variable
   | ATyCon   of type_constructor * aty list