diff --git a/sledge/lib/import/map.ml b/sledge/lib/import/map.ml
index 415b00fb6..e7c6cbb63 100644
--- a/sledge/lib/import/map.ml
+++ b/sledge/lib/import/map.ml
@@ -6,66 +6,7 @@
  *)
 
 open Import0
-
-module type S = sig
-  type key
-  type +'a t
-
-  val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
-  val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
-  val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
-  val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
-  val pp : key pp -> 'a pp -> 'a t pp
-
-  val pp_diff :
-       data_equal:('a -> 'a -> bool)
-    -> key pp
-    -> 'a pp
-    -> ('a * 'a) pp
-    -> ('a t * 'a t) pp
-
-  (* initial constructors *)
-  val empty : 'a t
-
-  (* constructors *)
-  val set : 'a t -> key:key -> data:'a -> 'a t
-  val add_exn : 'a t -> key:key -> data:'a -> 'a t
-  val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
-  val remove : 'a t -> key -> 'a t
-  val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
-
-  val merge :
-       'a t
-    -> 'b t
-    -> f:
-         (   key:key
-          -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
-          -> 'c option)
-    -> 'c t
-
-  val merge_skewed :
-    'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
-
-  val map : 'a t -> f:('a -> 'b) -> 'b t
-  val filter_keys : 'a t -> f:(key -> bool) -> 'a t
-  val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
-
-  (* queries *)
-  val is_empty : 'b t -> bool
-  val length : 'b t -> int
-  val mem : 'a t -> key -> bool
-  val find : 'a t -> key -> 'a option
-  val find_and_remove : 'a t -> key -> ('a * 'a t) option
-  val find_multi : 'a list t -> key -> 'a list
-  val data : 'a t -> 'a list
-  val to_alist : 'a t -> (key * 'a) list
-
-  (* traversals *)
-  val iter : 'a t -> f:('a -> unit) -> unit
-  val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
-  val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
-  val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
-end
+include Map_intf
 
 module Make (Key : OrderedType) : S with type key = Key.t = struct
   module M = Stdlib.Map.Make (Key)
diff --git a/sledge/lib/import/map.mli b/sledge/lib/import/map.mli
index a64666233..bc9dceeb7 100644
--- a/sledge/lib/import/map.mli
+++ b/sledge/lib/import/map.mli
@@ -6,65 +6,5 @@
  *)
 
 open Import0
-
-module type S = sig
-  type key
-  type +'a t
-
-  val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
-  val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
-  val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
-  val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
-  val pp : key pp -> 'a pp -> 'a t pp
-
-  val pp_diff :
-       data_equal:('a -> 'a -> bool)
-    -> key pp
-    -> 'a pp
-    -> ('a * 'a) pp
-    -> ('a t * 'a t) pp
-
-  (* initial constructors *)
-  val empty : 'a t
-
-  (* constructors *)
-  val set : 'a t -> key:key -> data:'a -> 'a t
-  val add_exn : 'a t -> key:key -> data:'a -> 'a t
-  val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
-  val remove : 'a t -> key -> 'a t
-  val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
-
-  val merge :
-       'a t
-    -> 'b t
-    -> f:
-         (   key:key
-          -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
-          -> 'c option)
-    -> 'c t
-
-  val merge_skewed :
-    'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
-
-  val map : 'a t -> f:('a -> 'b) -> 'b t
-  val filter_keys : 'a t -> f:(key -> bool) -> 'a t
-  val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
-
-  (* queries *)
-  val is_empty : 'b t -> bool
-  val length : 'b t -> int
-  val mem : 'a t -> key -> bool
-  val find : 'a t -> key -> 'a option
-  val find_and_remove : 'a t -> key -> ('a * 'a t) option
-  val find_multi : 'a list t -> key -> 'a list
-  val data : 'a t -> 'a list
-  val to_alist : 'a t -> (key * 'a) list
-
-  (* traversals *)
-  val iter : 'a t -> f:('a -> unit) -> unit
-  val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
-  val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
-  val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
-end
-
+include module type of Map_intf
 module Make (Key : OrderedType) : S with type key = Key.t
diff --git a/sledge/lib/import/map_intf.ml b/sledge/lib/import/map_intf.ml
new file mode 100644
index 000000000..850b9eb8e
--- /dev/null
+++ b/sledge/lib/import/map_intf.ml
@@ -0,0 +1,68 @@
+(*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *)
+
+open Import0
+
+module type S = sig
+  type key
+  type +'a t
+
+  val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
+  val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
+  val sexp_of_t : ('a -> Sexp.t) -> 'a t -> Sexp.t
+  val t_of_sexp : (Sexp.t -> key) -> (Sexp.t -> 'a) -> Sexp.t -> 'a t
+  val pp : key pp -> 'a pp -> 'a t pp
+
+  val pp_diff :
+       data_equal:('a -> 'a -> bool)
+    -> key pp
+    -> 'a pp
+    -> ('a * 'a) pp
+    -> ('a t * 'a t) pp
+
+  (* initial constructors *)
+  val empty : 'a t
+
+  (* constructors *)
+  val set : 'a t -> key:key -> data:'a -> 'a t
+  val add_exn : 'a t -> key:key -> data:'a -> 'a t
+  val add_multi : 'a list t -> key:key -> data:'a -> 'a list t
+  val remove : 'a t -> key -> 'a t
+  val update : 'a t -> key -> f:('a option -> 'a) -> 'a t
+
+  val merge :
+       'a t
+    -> 'b t
+    -> f:
+         (   key:key
+          -> [`Both of 'a * 'b | `Left of 'a | `Right of 'b]
+          -> 'c option)
+    -> 'c t
+
+  val merge_skewed :
+    'a t -> 'a t -> combine:(key:key -> 'a -> 'a -> 'a) -> 'a t
+
+  val map : 'a t -> f:('a -> 'b) -> 'b t
+  val filter_keys : 'a t -> f:(key -> bool) -> 'a t
+  val filter_mapi : 'a t -> f:(key:key -> data:'a -> 'b option) -> 'b t
+
+  (* queries *)
+  val is_empty : 'b t -> bool
+  val length : 'b t -> int
+  val mem : 'a t -> key -> bool
+  val find : 'a t -> key -> 'a option
+  val find_and_remove : 'a t -> key -> ('a * 'a t) option
+  val find_multi : 'a list t -> key -> 'a list
+  val data : 'a t -> 'a list
+  val to_alist : 'a t -> (key * 'a) list
+
+  (* traversals *)
+  val iter : 'a t -> f:('a -> unit) -> unit
+  val iteri : 'a t -> f:(key:key -> data:'a -> unit) -> unit
+  val for_alli : 'a t -> f:(key:key -> data:'a -> bool) -> bool
+  val fold : 'a t -> init:'s -> f:(key:key -> data:'a -> 's -> 's) -> 's
+end