diff --git a/include/nuttx/net/netconfig.h b/include/nuttx/net/netconfig.h
index 4c6f58d15b..aeea16b4e1 100644
--- a/include/nuttx/net/netconfig.h
+++ b/include/nuttx/net/netconfig.h
@@ -139,7 +139,7 @@
 #elif defined(CONFIG_NET_SLIP)
    /* There is no link layer header with SLIP */
 
-#  ifdef CONFIG_NET_IPv4
+#  ifndef CONFIG_NET_IPv4
 #    error SLIP requires IPv4 support
 #  endif