diff --git a/_CoqProject b/_CoqProject
index 21c4898b874cb3c64f46ea48d4386f16fbcc45fe..332e5c76b38017445903d0cdaafe003b8cca0ba9 100644
--- a/_CoqProject
+++ b/_CoqProject
@@ -53,7 +53,6 @@ theories/typing/lib/fake_shared_box.v
 theories/typing/lib/cell.v
 theories/typing/lib/spawn.v
 theories/typing/lib/rc.v
-theories/typing/lib/mutex.v
 theories/typing/lib/refcell/refcell.v
 theories/typing/lib/refcell/ref.v
 theories/typing/lib/refcell/refmut.v