diff --git a/src/sigar_win32ish.c b/src/sigar_win32ish.c
index 01971917..b7363e71 100644
--- a/src/sigar_win32ish.c
+++ b/src/sigar_win32ish.c
@@ -86,7 +86,7 @@ static void hwaddr_lookup(sigar_net_interface_config_t *ifconfig, int num)
     memset(&ncb.ncb_callname[1], ' ',
            sizeof(ncb.ncb_callname)-1);
 
-    ncb.ncb_callname[sizeof(ncb.ncb_callname)] = '\0';
+    ncb.ncb_callname[sizeof(ncb.ncb_callname)-1] = '\0';
 
     ncb.ncb_buffer = (unsigned char *)&adapter;
     ncb.ncb_length = sizeof(adapter);