diff --git a/src/config/index.ts b/src/config/index.ts
index 2060b62..f4a2eee 100644
--- a/src/config/index.ts
+++ b/src/config/index.ts
@@ -69,7 +69,7 @@ export function loadConfig(
     readOnlyEnv === "yes";
 
   const portArg = parseCliArg(argv, "--port");
-  const portStr = portArg ?? env.PORT;
+  const portStr = portArg ?? env.PORT ?? env.HOST_PORT;
   let port: number | undefined;
   if (portStr !== undefined && portStr.trim() !== "") {
     const parsed = parseInt(portStr.trim(), 10);
diff --git a/tests/config.test.ts b/tests/config.test.ts
index ec6b6d4..0b0dd75 100644
--- a/tests/config.test.ts
+++ b/tests/config.test.ts
@@ -82,6 +82,18 @@ describe("Configuration Loader (HTTP & Stdio Support)", () => {
     expect(config.apiKey).toBeUndefined();
   });
 
+  test("loads HTTP configuration when HOST_PORT is set as fallback without PORT", () => {
+    process.env.OPENPROJECT_BASE_URL = "https://openproject.example.com";
+    delete process.env.OPENPROJECT_API_KEY;
+    delete process.env.PORT;
+    process.env.HOST_PORT = "3000";
+
+    const config = loadConfig();
+    expect(config.baseUrl).toBe("https://openproject.example.com");
+    expect(config.port).toBe(3000);
+    expect(config.apiKey).toBeUndefined();
+  });
+
   test("loads HTTP configuration with API key when provided", () => {
     process.env.OPENPROJECT_BASE_URL = "https://openproject.example.com";
     process.env.OPENPROJECT_API_KEY = "test-key";