diff --git a/README.md b/README.md
index 8a51938a..04abc09b 100644
--- a/README.md
+++ b/README.md
@@ -103,8 +103,16 @@ handling logic.
 		if envPort := os.Getenv("PORT"); envPort != "" {
 			port = envPort
 		}
-		if err := funcframework.Start(port); err != nil {
-			log.Fatalf("funcframework.Start: %v\n", err)
+		
+		// By default, listen on all interfaces. If testing locally, run with 
+		// LOCAL_ONLY=true to avoid triggering firewall warnings and 
+		// exposing the server outside of your own machine.
+		hostname := ""
+		if localOnly := os.Getenv("LOCAL_ONLY"); localOnly == "true" {
+			hostname = "127.0.0.1"
+		} 
+		if err := funcframework.StartHostPort(hostname, port); err != nil {
+			log.Fatalf("funcframework.StartHostPort: %v\n", err)
 		}
 	}
 	```
@@ -113,8 +121,7 @@ handling logic.
 
 1. Start the local development server:
 	```sh
-	export FUNCTION_TARGET=HelloWorld
-	go run cmd/main.go
+	FUNCTION_TARGET=HelloWorld LOCAL_ONLY=true go run cmd/main.go
 	# Output: Serving function: HelloWorld
 	```
 
diff --git a/funcframework/framework.go b/funcframework/framework.go
index 2aeb6b1d..335daf76 100644
--- a/funcframework/framework.go
+++ b/funcframework/framework.go
@@ -101,11 +101,16 @@ func RegisterCloudEventFunctionContext(ctx context.Context, path string, fn func
 
 // Start serves an HTTP server with registered function(s).
 func Start(port string) error {
+	return StartHostPort("", port)
+}
+
+// StartHostPort serves an HTTP server with registered function(s) on the given host and port.
+func StartHostPort(hostname, port string) error {
 	server, err := initServer()
 	if err != nil {
 		return err
 	}
-	return http.ListenAndServe(":"+port, server)
+	return http.ListenAndServe(fmt.Sprintf("%s:%s", hostname, port), server)
 }
 
 func initServer() (*http.ServeMux, error) {