diff --git a/scripts/addr_class_allowlist.txt b/scripts/addr_class_allowlist.txt
index b118618296..8c8ce6254c 100644
--- a/scripts/addr_class_allowlist.txt
+++ b/scripts/addr_class_allowlist.txt
@@ -136,6 +136,7 @@ crates/perry-runtime/src/object/global_this/ | * | pre-existing GcHeader probe p
 crates/perry-runtime/src/object/class_registry/ | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of class_registry.rs)
 crates/perry-runtime/src/object/descriptor_state.rs | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of object/mod.rs)
 crates/perry-runtime/src/object/to_string_tag.rs | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of object/mod.rs)
+crates/perry-runtime/src/object/collection_proto_thunks.rs | * | GcHeader obj_type probe guarded by is_above_handle_band + is_valid_obj_ptr (magnitude-classified before the deref); migrate to addr_class::try_read_gc_header in a follow-up (added in #6659)
 crates/perry-runtime/src/symbol/ | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of symbol.rs)
 crates/perry-runtime/src/typedarray/ | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of typedarray/mod.rs)
 crates/perry-runtime/src/process/ | * | pre-existing GcHeader probe predating addr_class; address validated by call-site guards (magnitude/registry/is_valid_obj_ptr) -- migrate to addr_class::try_read_gc_header in a follow-up (split of process.rs)