diff --git a/src/unix/cygwin/mod.rs b/src/unix/cygwin/mod.rs
index e190e18f4cd63..0c093a4c17726 100644
--- a/src/unix/cygwin/mod.rs
+++ b/src/unix/cygwin/mod.rs
@@ -1038,6 +1038,7 @@ pub const TIOCM_RTS: c_int = 0x004;
 pub const TIOCM_CTS: c_int = 0x020;
 pub const TIOCM_CAR: c_int = 0x040;
 pub const TIOCM_RNG: c_int = 0x080;
+pub const TIOCM_DSR: c_int = 0x100;
 pub const TIOCM_CD: c_int = TIOCM_CAR;
 pub const TIOCM_RI: c_int = TIOCM_RNG;
 pub const TCOOFF: c_int = 0;