diff --git a/docs/src/main/asciidoc/funqy-gcp-functions.adoc b/docs/src/main/asciidoc/funqy-gcp-functions.adoc
index 5a6b9fa9329dd..165a2a3900a15 100644
--- a/docs/src/main/asciidoc/funqy-gcp-functions.adoc
+++ b/docs/src/main/asciidoc/funqy-gcp-functions.adoc
@@ -385,6 +385,8 @@ To use it, you must add the following test dependency in your `pom.xml`.
 This extension provides a `@WithFunction` annotation that can be used to annotate `@QuarkusTest` test cases to start a Cloud Function invoker before you test cases and stop it at the end.
 This annotation must be configured with the type of the function you want to launch, and optionally the name of the function in case you have multiple functions inside your application.
 
+The default Quarkus test port configuration (`quarkus.http.test-port`) will be honored and if you set it to 0 a random port will be assigned to the function invoker.
+
 === Background Functions - PubSub
 
 [source,java]
diff --git a/docs/src/main/asciidoc/gcp-functions.adoc b/docs/src/main/asciidoc/gcp-functions.adoc
index d0ce3a5a1fe97..151d99319e314 100644
--- a/docs/src/main/asciidoc/gcp-functions.adoc
+++ b/docs/src/main/asciidoc/gcp-functions.adoc
@@ -490,6 +490,8 @@ To use it, you must add the following test dependency in your `pom.xml`.
 This extension provides a `@WithFunction` annotation that can be used to annotate `@QuarkusTest` test cases to start a Cloud Function invoker before you test cases and stop it at the end.
 This annotation must be configured with the type of the function you want to launch, and optionally the name of the function in case you have multiple functions inside your application.
 
+The default Quarkus test port configuration (`quarkus.http.test-port`) will be honored and if you set it to 0 a random port will be assigned to the function invoker.
+
 === The HttpFunction
 
 [source,java]
diff --git a/integration-tests/google-cloud-functions/src/test/java/io/quarkus/gcp/function/test/HttpFunctionRandomPortTestCase.java b/integration-tests/google-cloud-functions/src/test/java/io/quarkus/gcp/function/test/HttpFunctionRandomPortTestCase.java
new file mode 100644
index 0000000000000..62bc600f3ff76
--- /dev/null
+++ b/integration-tests/google-cloud-functions/src/test/java/io/quarkus/gcp/function/test/HttpFunctionRandomPortTestCase.java
@@ -0,0 +1,31 @@
+package io.quarkus.gcp.function.test;
+
+import static io.restassured.RestAssured.when;
+import static org.hamcrest.Matchers.is;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import io.quarkus.google.cloud.functions.test.FunctionType;
+import io.quarkus.google.cloud.functions.test.WithFunction;
+import io.quarkus.test.junit.QuarkusTest;
+
+@QuarkusTest
+@WithFunction(FunctionType.HTTP)
+class HttpFunctionRandomPortTestCase {
+
+    @BeforeAll
+    public static void setup() {
+        System.setProperty("quarkus.http.test-port", "0");
+    }
+
+    @Test
+    public void test() {
+        // test the function using RestAssured
+        when()
+                .get()
+                .then()
+                .statusCode(200)
+                .body(is("Hello World!"));
+    }
+}
diff --git a/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/CloudFunctionsInvoker.java b/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/CloudFunctionsInvoker.java
index 7398177930c74..efe8648db5351 100644
--- a/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/CloudFunctionsInvoker.java
+++ b/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/CloudFunctionsInvoker.java
@@ -11,8 +11,12 @@ class CloudFunctionsInvoker {
     }
 
     CloudFunctionsInvoker(FunctionType functionType, int port) {
+        int realPort = port == 0 ? SocketUtil.findAvailablePort() : port;
+        if (realPort != port) {
+            System.setProperty("quarkus.http.test-port", String.valueOf(realPort));
+        }
         this.invoker = new Invoker(
-                port,
+                realPort,
                 functionType.getTarget(),
                 functionType.getSignatureType(),
                 Thread.currentThread().getContextClassLoader());
diff --git a/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/SocketUtil.java b/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/SocketUtil.java
new file mode 100644
index 0000000000000..cc29160ef51f0
--- /dev/null
+++ b/test-framework/google-cloud-functions/src/main/java/io/quarkus/google/cloud/functions/test/SocketUtil.java
@@ -0,0 +1,29 @@
+package io.quarkus.google.cloud.functions.test;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+
+// copied from the mailer extension: io.quarkus.mailer.runtime.SocketUtil
+final class SocketUtil {
+
+    private SocketUtil() {
+    }
+
+    static int findAvailablePort() {
+        ServerSocket serverSocket = null;
+        try {
+            serverSocket = new ServerSocket(0);
+            return serverSocket.getLocalPort();
+        } catch (Exception e) {
+            // return a default port
+            return 25347;
+        } finally {
+            if (serverSocket != null) {
+                try {
+                    serverSocket.close();
+                } catch (IOException e) {
+                }
+            }
+        }
+    }
+}