diff --git a/_CoqProject b/_CoqProject
index 16fda88572bd3a96b697c6dfcff9e4e6a38bbefd..dc118e31215b546b05796e7a1e626d0e01983952 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -55,6 +55,7 @@ theories/typing/lib/swap.v
 theories/typing/lib/take_mut.v
 theories/typing/lib/spawn.v
 theories/typing/lib/join.v
+theories/typing/lib/arc.v
 theories/typing/lib/mutex/mutex.v
 theories/typing/lib/mutex/mutexguard.v
 theories/typing/lib/rc/rc.v