diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index 005c957046..1bbb91bfeb 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -146,11 +146,10 @@ NOTEST=\
 NOBENCH=\
 	container/vector\
 
-TEST=\
-	$(filter-out $(NOTEST),$(DIRS))
-
-BENCH=\
-	$(filter-out $(NOBENCH),$(TEST))
+# Disable tests that depend on an external network.
+ifeq ($(DISABLE_NET_TESTS),1)
+NOTEST+=http net
+endif
 
 # Disable tests that NaCl cannot run yet.
 ifeq ($(GOOS),nacl)
@@ -172,6 +171,12 @@ NOTEST+=time         # no syscall.Kill, syscall.SIGCHLD for sleep tests
 NOTEST+=websocket    # no network
 endif
 
+TEST=\
+	$(filter-out $(NOTEST),$(DIRS))
+
+BENCH=\
+	$(filter-out $(NOBENCH),$(TEST))
+
 clean.dirs: $(addsuffix .clean, $(DIRS))
 install.dirs: $(addsuffix .install, $(DIRS))
 nuke.dirs: $(addsuffix .nuke, $(DIRS))
diff --git a/src/pkg/netchan/netchan_test.go b/src/pkg/netchan/netchan_test.go
index ca3f4d4c79..01fc0f3272 100644
--- a/src/pkg/netchan/netchan_test.go
+++ b/src/pkg/netchan/netchan_test.go
@@ -72,7 +72,7 @@ func importSend(imp *Importer, t *testing.T) {
 }
 
 func TestExportSendImportReceive(t *testing.T) {
-	exp, err := NewExporter("tcp", ":0")
+	exp, err := NewExporter("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatal("new exporter:", err)
 	}
@@ -85,7 +85,7 @@ func TestExportSendImportReceive(t *testing.T) {
 }
 
 func TestExportReceiveImportSend(t *testing.T) {
-	exp, err := NewExporter("tcp", ":0")
+	exp, err := NewExporter("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatal("new exporter:", err)
 	}
@@ -98,7 +98,7 @@ func TestExportReceiveImportSend(t *testing.T) {
 }
 
 func TestClosingExportSendImportReceive(t *testing.T) {
-	exp, err := NewExporter("tcp", ":0")
+	exp, err := NewExporter("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatal("new exporter:", err)
 	}
diff --git a/src/pkg/rpc/server_test.go b/src/pkg/rpc/server_test.go
index 3196891d25..edf35e6c9f 100644
--- a/src/pkg/rpc/server_test.go
+++ b/src/pkg/rpc/server_test.go
@@ -55,7 +55,7 @@ func (t *Arith) Error(args *Args, reply *Reply) os.Error {
 func startServer() {
 	Register(new(Arith))
 
-	l, e := net.Listen("tcp", ":0") // any available address
+	l, e := net.Listen("tcp", "127.0.0.1:0") // any available address
 	if e != nil {
 		log.Exitf("net.Listen tcp :0: %v", e)
 	}
@@ -64,7 +64,7 @@ func startServer() {
 	go Accept(l)
 
 	HandleHTTP()
-	l, e = net.Listen("tcp", ":0") // any available address
+	l, e = net.Listen("tcp", "127.0.0.1:0") // any available address
 	if e != nil {
 		log.Stderrf("net.Listen tcp :0: %v", e)
 		os.Exit(1)
diff --git a/src/pkg/websocket/websocket_test.go b/src/pkg/websocket/websocket_test.go
index 0762fca699..df7e9f4dae 100644
--- a/src/pkg/websocket/websocket_test.go
+++ b/src/pkg/websocket/websocket_test.go
@@ -20,7 +20,7 @@ var serverAddr string
 func echoServer(ws *Conn) { io.Copy(ws, ws) }
 
 func startServer() {
-	l, e := net.Listen("tcp", ":0") // any available address
+	l, e := net.Listen("tcp", "127.0.0.1:0") // any available address
 	if e != nil {
 		log.Exitf("net.Listen tcp :0 %v", e)
 	}