1 files changed, 1 insertions, 1 deletions
diff --git a/byterun/weak.c b/byterun/weak.c
index e85468601..c6c4a223f 100644
--- a/byterun/weak.c
+++ b/byterun/weak.c
@@ -70,7 +70,7 @@ CAMLprim value caml_weak_set (value ar, value n, value el)
   if (offset < 1 || offset >= Wosize_val (ar)){
     caml_invalid_argument ("Weak.set");
   }
-  if (el != None_val){
+  if (el != None_val && Is_block (el)){
                                               Assert (Wosize_val (el) == 1);
     do_set (ar, offset, Field (el, 0));
   }else{