diff --git a/src/lib.rs b/src/lib.rs
index 1d6a5f2768..e44376d4ea 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1188,6 +1188,10 @@ pub mod protocol {
         }
     }
 
-    pub const O_CLOEXEC: usize = syscall::flag::O_CLOEXEC;
+    // Literal, NOT `syscall::flag::O_CLOEXEC`: this `protocol` module is built
+    // standalone by relibc (default-features=false, features=["protocol"]), so
+    // the optional `redox_syscall`/`base`/`libc` crates are NOT linked here.
+    // 0x0100_0000 is exactly syscall's O_CLOEXEC value.
+    pub const O_CLOEXEC: usize = 0x0100_0000;
     pub const F_DUPFD_CLOEXEC: usize = 5;
 }