diff --git a/include/glibtop/interfaces.h b/include/glibtop/interfaces.h
index 70876918..a8ff5c3e 100644
--- a/include/glibtop/interfaces.h
+++ b/include/glibtop/interfaces.h
@@ -54,6 +54,7 @@ enum _glibtop_interface {
     GLIBTOP_INTERFACE_LOOPBACK,
     GLIBTOP_INTERFACE_DUMMY,
     GLIBTOP_INTERFACE_PPP,
+    GLIBTOP_INTERFACE_ISDN
 };
 
 enum {