diff --git a/Changes b/Changes
index 84e8cabed..f982cc980 100644
--- a/Changes
+++ b/Changes
@@ -534,6 +534,10 @@ Working version
 - #9927: Restore Cygwin64 support.
   (David Allsopp, review by Xavier Leroy)
 
+- #9940: Fix unboxing of allocated constants from other compilation units
+  (Vincent Laviron, report by Stephen Dolan, review by Xavier Leroy and
+  Stephen Dolan)
+
 
 OCaml 4.11.1
 ------------
diff --git a/asmcomp/cmmgen.ml b/asmcomp/cmmgen.ml
index bda1ee982..77d29951c 100644
--- a/asmcomp/cmmgen.ml
+++ b/asmcomp/cmmgen.ml
@@ -178,7 +178,10 @@ let rec expr_size env = function
 let transl_constant dbg = function
   | Uconst_int n ->
       int_const dbg n
-  | Uconst_ref (label, _) ->
+  | Uconst_ref (label, def_opt) ->
+      Option.iter
+        (fun def -> Cmmgen_state.add_structured_constant label def)
+        def_opt;
       Cconst_symbol (label, dbg)
 
 let emit_constant cst cont =
diff --git a/asmcomp/cmmgen_state.ml b/asmcomp/cmmgen_state.ml
index 595aba4d9..9d6622352 100644
--- a/asmcomp/cmmgen_state.ml
+++ b/asmcomp/cmmgen_state.ml
@@ -76,6 +76,9 @@ let set_structured_constants l =
     )
     l
 
+let add_structured_constant sym cst =
+  Hashtbl.replace state.structured_constants sym cst
+
 let get_structured_constant s =
   Hashtbl.find_opt state.structured_constants s
 
diff --git a/asmcomp/cmmgen_state.mli b/asmcomp/cmmgen_state.mli
index 306f55d5c..f10073924 100644
--- a/asmcomp/cmmgen_state.mli
+++ b/asmcomp/cmmgen_state.mli
@@ -41,5 +41,7 @@ val no_more_functions : unit -> bool
 
 val set_structured_constants : Clambda.preallocated_constant list -> unit
 
+val add_structured_constant : string -> Clambda.ustructured_constant -> unit
+
 (* Also looks up using Compilenv.structured_constant_of_symbol *)
 val structured_constant_of_sym : string -> Clambda.ustructured_constant option