diff --git a/include/netutils/ifc.h b/include/netutils/ifc.h
index 67a4a45..9079ab4 100644
--- a/include/netutils/ifc.h
+++ b/include/netutils/ifc.h
@@ -66,6 +66,8 @@
                          uint32_t prefixLength, in_addr_t gateway,
                          in_addr_t dns1, in_addr_t dns2);
 
+extern in_addr_t prefixLengthToIpv4Netmask(int prefix_length);
+
 __END_DECLS
 
 #endif /* _NETUTILS_IFC_H_ */