diff --git a/src/evalvars.c b/src/evalvars.c
index 28516c1..20223c8 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -4761,13 +4761,16 @@
 	{
 	    aco_save_T	aco;
 
-	    // set curbuf to be our buf, temporarily
+	    // Set curbuf to be our buf, temporarily.
 	    aucmd_prepbuf(&aco, buf);
+	    if (curbuf == buf)
+	    {
+		// Only when it worked to set "curbuf".
+		set_option_from_tv(varname + 1, varp);
 
-	    set_option_from_tv(varname + 1, varp);
-
-	    // reset notion of buffer
-	    aucmd_restbuf(&aco);
+		// reset notion of buffer
+		aucmd_restbuf(&aco);
+	    }
 	}
 	else
 	{