diff --git a/src/ctx.rs b/src/ctx.rs
index 3f4d9d5cf9..b86bfa2bd7 100644
--- a/src/ctx.rs
+++ b/src/ctx.rs
@@ -135,7 +135,7 @@ impl WasiCtxBuilder {
             let mut fe = FdEntry::from(dir)?;
             fe.preopen_path = Some(guest_path);
             self.fds.insert(preopen_fd, fe);
-            preopen_fd += 1;
+            preopen_fd = preopen_fd.checked_add(1).ok_or(Error::ENFILE)?;
         }
 
         let env = self