diff --git a/addons/xterm-addon-fit/typings/xterm-addon-fit.d.ts b/addons/xterm-addon-fit/typings/xterm-addon-fit.d.ts
index c3b0b4af..2d1b8f1d 100644
--- a/addons/xterm-addon-fit/typings/xterm-addon-fit.d.ts
+++ b/addons/xterm-addon-fit/typings/xterm-addon-fit.d.ts
@@ -35,7 +35,7 @@ declare module 'xterm-addon-fit' {
     /**
      * Gets the proposed dimensions that will be used for a fit.
      */
-    public proposeDimensions(): ITerminalDimensions;
+    public proposeDimensions(): ITerminalDimensions | undefined;
   }
 
   /**