diff --git a/src/vim9.h b/src/vim9.h
index 3ab1c5a..b32dbea 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -25,6 +25,7 @@
     ISN_EXECUTE,    // :execute with isn_arg.number items on top of stack
     ISN_ECHOMSG,    // :echomsg with isn_arg.number items on top of stack
     ISN_ECHOCONSOLE, // :echoconsole with isn_arg.number items on top of stack
+    ISN_ECHOWINDOW, // :echowindow with isn_arg.number items on top of stack
     ISN_ECHOERR,    // :echoerr with isn_arg.number items on top of stack
     ISN_RANGE,	    // compute range from isn_arg.string, push to stack
     ISN_SUBSTITUTE, // :s command with expression