diff --git a/src/option.c b/src/option.c
index d93d385..3fa3b1c 100644
--- a/src/option.c
+++ b/src/option.c
@@ -3898,6 +3898,7 @@
 	args.os_oldval.boolean = old_value;
 	args.os_newval.boolean = value;
 	args.os_doskip = FALSE;
+	args.os_errbuf = NULL;
 	errmsg = options[opt_idx].opt_did_set_cb(&args);
 	if (args.os_doskip)
 	    return errmsg;
@@ -4669,6 +4670,7 @@
 	args.os_flags = opt_flags;
 	args.os_oldval.number = old_value;
 	args.os_newval.number = value;
+	args.os_errbuf = NULL;
 	errmsg = options[opt_idx].opt_did_set_cb(&args);
     }