diff --git a/tools/dumpobj.ml b/tools/dumpobj.ml
index 3f3968702..b2fefad8b 100644
--- a/tools/dumpobj.ml
+++ b/tools/dumpobj.ml
@@ -23,6 +23,7 @@ open Location
 open Obj
 open Opcodes
 open Opnames
+open Cmo_format
 open Printf
 
 (* Read signed and unsigned integers *)