diff --git a/src/number.rs b/src/number.rs
index 719c8af..ef3dbd7 100644
--- a/src/number.rs
+++ b/src/number.rs
@@ -18,6 +18,7 @@ pub const SYS_UNLINK: usize =   SYS_CLASS_PATH | 10;
 
 pub const SYS_CLOSE: usize =    SYS_CLASS_FILE | 6;
 pub const SYS_DUP: usize =      SYS_CLASS_FILE | SYS_RET_FILE | 41;
+pub const SYS_DUP2: usize =      SYS_CLASS_FILE | SYS_RET_FILE | 63;
 pub const SYS_READ: usize =     SYS_CLASS_FILE | SYS_ARG_MSLICE | 3;
 pub const SYS_WRITE: usize =    SYS_CLASS_FILE | SYS_ARG_SLICE | 4;
 pub const SYS_LSEEK: usize =    SYS_CLASS_FILE | 19;