diff --git a/infer/src/absint/ProcCfg.ml b/infer/src/absint/ProcCfg.ml
index 29cb0c609..0bf5ca08b 100644
--- a/infer/src/absint/ProcCfg.ml
+++ b/infer/src/absint/ProcCfg.ml
@@ -74,9 +74,11 @@ module DefaultNode = struct
 end
 
 module InstrNode = struct
-  type t = Procdesc.Node.t * int
+  type instr_index = int [@@deriving compare]
 
-  type id = Procdesc.Node.id * int [@@deriving compare]
+  type t = Procdesc.Node.t * instr_index
+
+  type id = Procdesc.Node.id * instr_index [@@deriving compare]
 
   let kind (t, _) = Procdesc.Node.get_kind t
 
diff --git a/infer/src/absint/ProcCfg.mli b/infer/src/absint/ProcCfg.mli
index bca572c29..99cb0d9b0 100644
--- a/infer/src/absint/ProcCfg.mli
+++ b/infer/src/absint/ProcCfg.mli
@@ -82,7 +82,13 @@ end
 
 module DefaultNode : Node with type t = Procdesc.Node.t and type id = Procdesc.Node.id
 
-module InstrNode : Node with type t = Procdesc.Node.t * int and type id = Procdesc.Node.id * int
+module InstrNode : sig
+  type instr_index
+
+  include Node
+          with type t = Procdesc.Node.t * instr_index
+           and type id = Procdesc.Node.id * instr_index
+end
 
 (** Forward CFG with no exceptional control-flow *)
 module Normal :