diff --git a/src/structs.h b/src/structs.h
index 6d9dcbb..de02bc6 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4969,7 +4969,7 @@
     // message (when it is not NULL).
     char	*os_errbuf;
     // length of the error buffer
-    int		os_errbuflen;
+    size_t	os_errbuflen;
 } optset_T;
 
 /*