diff --git a/infer/src/backend/dom.ml b/infer/src/backend/dom.ml
index abf16f6d8..28eb024e9 100644
--- a/infer/src/backend/dom.ml
+++ b/infer/src/backend/dom.ml
@@ -16,23 +16,6 @@ module F = Format
 let (++) = Sil.Int.add
 let (--) = Sil.Int.sub
 
-(** {2 Object representing the status of the join operation} *)
-
-module JoinState : sig
-
-  type mode = Pre | Post
-  val get_footprint : unit -> bool
-  val set_footprint : bool -> unit
-
-end = struct
-
-  type mode = Pre | Post
-  let footprint = ref false (* set to true when we are doing join of footprints *)
-  let get_footprint () = !footprint
-  let set_footprint b = footprint := b
-
-end
-
 (** {2 Utility functions for ids} *)
 
 let can_rename id =
diff --git a/infer/src/backend/joinState.ml b/infer/src/backend/joinState.ml
new file mode 100644
index 000000000..d3ce0834b
--- /dev/null
+++ b/infer/src/backend/joinState.ml
@@ -0,0 +1,21 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+(** Object representing the status of the join operation *)
+
+type mode =
+  | Pre
+  | Post
+
+(** set to true when we are doing join of footprints *)
+let footprint = ref false
+
+let get_footprint () = !footprint
+
+let set_footprint b = footprint := b
diff --git a/infer/src/backend/joinState.mli b/infer/src/backend/joinState.mli
new file mode 100644
index 000000000..f74e2fe64
--- /dev/null
+++ b/infer/src/backend/joinState.mli
@@ -0,0 +1,17 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+(** Object representing the status of the join operation *)
+
+type mode =
+  | Pre
+  | Post
+
+val get_footprint : unit -> bool
+val set_footprint : bool -> unit