diff --git a/examples/tcp_echo_server.v b/examples/tcp_echo_server.v
index a00e2e1..eda4b5a 100644
--- a/examples/tcp_echo_server.v
+++ b/examples/tcp_echo_server.v
@@ -1,4 +1,5 @@
 import netio
+import netio.protocol
 
 fn main() {
 	// This is only for examples_test.v
@@ -8,7 +9,8 @@ fn main() {
 	listen_addr := netio.SocketAddr.new_ipv4([..]u8[127, 0, 0, 1], 1088)
 
 	// Create server socket.
-	socket := netio.Socket.new(netio.af_inet, netio.sock_stream, 0)!
+	socket := netio.Socket.new(netio.af_inet, netio.sock_stream,
+		protocol.protocol_by_name('tcp')!.number)!
 
 	// Close server socket on exit.
 	defer {
diff --git a/protocol/protocol.c.v b/protocol/protocol.c.v
index 6c7d16a..399ffcf 100644
--- a/protocol/protocol.c.v
+++ b/protocol/protocol.c.v
@@ -4,6 +4,8 @@ module protocol
 import os
 import sync
 
+#include <netdb.h>
+
 // Mutex for accessing to protocol entries via getprotoent(3).
 __global netio_proto_mutex &sync.Mutex
 
@@ -35,7 +37,7 @@ pub:
 	number  int      // The protocol number.
 }
 
-fn make_proto(ent C.protoent) ProtocolEntry {
+fn make_proto(ent &C.protoent) ProtocolEntry {
 	mut aliases := []string{}
 	if unsafe { ent.p_aliases[0] != nil } {
 		mut ptr := *ent.p_aliases
diff --git a/protocol/protocol_test.v b/protocol/protocol_test.v
new file mode 100644
index 0000000..3ea1ac4
--- /dev/null
+++ b/protocol/protocol_test.v
@@ -0,0 +1,14 @@
+import netio.protocol
+
+fn test_protocols() {
+	assert protocol.protocols().len > 0
+}
+
+fn test_protocol_by_name() {
+	assert protocol.protocol_by_name('tcp')!.aliases == ['TCP']
+}
+
+fn test_protocol_by_number() {
+	tcp_proto := protocol.protocol_by_name('tcp')!
+	assert protocol.protocol_by_number(tcp_proto.number)!.name == 'tcp'
+}