diff --git a/src/structs.h b/src/structs.h
index 4e081b8..6d9dcbb 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4968,6 +4968,8 @@
     // is parameterized, then the "os_errbuf" buffer is used to store the error
     // message (when it is not NULL).
     char	*os_errbuf;
+    // length of the error buffer
+    int		os_errbuflen;
 } optset_T;
 
 /*