diff --git a/ssh2/index.d.ts b/ssh2/index.d.ts
index 72b6200f21..c8df971ce8 100644
--- a/ssh2/index.d.ts
+++ b/ssh2/index.d.ts
@@ -1087,7 +1087,7 @@ export interface PseudoTtyInfo {
 }
 
 export interface TerminalModes {
-    [mode: string]: number;
+    [mode: string]: number|undefined;
     /** Interrupt character; `255` if none. Not all of these characters are supported on all systems. */
     VINTR?: number;
     /** The quit character (sends `SIGQUIT` signal on POSIX systems). */
@@ -1555,4 +1555,4 @@ export interface SFTPWrapper extends events.EventEmitter {
     on(event: "continue", listener: () => void): this;
 
     on(event: string | symbol, listener: Function): this;
-}
\ No newline at end of file
+}