diff --git a/packages/modules/localstack/src/localstack-container.test.ts b/packages/modules/localstack/src/localstack-container.test.ts
index bfb39676d..c690bf04b 100644
--- a/packages/modules/localstack/src/localstack-container.test.ts
+++ b/packages/modules/localstack/src/localstack-container.test.ts
@@ -110,4 +110,19 @@ describe("LocalStackContainer", { timeout: 180_000 }, () => {
     expect(exitCode).toBe(0);
     expect(output).toContain(`${LABEL_TESTCONTAINERS_SESSION_ID}=${sessionId}`);
   });
+
+  it("should concatenate sessionId label to LAMBDA_DOCKER_FLAGS", async () => {
+    const container = await new LocalstackContainer()
+      .withEnvironment({
+        LAMBDA_DOCKER_FLAGS: `-l mylabel=myvalue`,
+      })
+      .start();
+    const sessionId = container.getLabels()[LABEL_TESTCONTAINERS_SESSION_ID];
+
+    const { output, exitCode } = await container.exec(["printenv", "LAMBDA_DOCKER_FLAGS"]);
+
+    expect(exitCode).toBe(0);
+    expect(output).toContain(`${LABEL_TESTCONTAINERS_SESSION_ID}=${sessionId}`);
+    expect(output).toContain(`mylabel=myvalue`);
+  });
 });
diff --git a/packages/modules/localstack/src/localstack-container.ts b/packages/modules/localstack/src/localstack-container.ts
index c0ed1f394..7a5180f72 100644
--- a/packages/modules/localstack/src/localstack-container.ts
+++ b/packages/modules/localstack/src/localstack-container.ts
@@ -42,7 +42,10 @@ export class LocalstackContainer extends GenericContainer {
   private async flagLambdaSessionId(): Promise<void> {
     const client = await getContainerRuntimeClient();
     const reaper = await getReaper(client);
-    this.withEnvironment({ LAMBDA_DOCKER_FLAGS: `-l ${LABEL_TESTCONTAINERS_SESSION_ID}=${reaper.sessionId}` });
+
+    this.withEnvironment({
+      LAMBDA_DOCKER_FLAGS: `${this.environment["LAMBDA_DOCKER_FLAGS"] ?? ""} -l ${LABEL_TESTCONTAINERS_SESSION_ID}=${reaper.sessionId}`,
+    });
   }
 
   protected override async beforeContainerCreated(): Promise<void> {