diff --git a/_CoqProject b/_CoqProject
index 98f2232e2c2524ba9bc540822f4474253bbd1072..700e7c386dddbe3cb9e220209bda79c7196039b7 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -21,6 +21,7 @@ theories/lang/new_delete.v
 theories/lang/swap.v
 theories/lang/lock.v
 theories/lang/spawn.v
+theories/lang/arc.v
 theories/typing/base.v
 theories/typing/lft_contexts.v
 theories/typing/type.v