diff --git a/tests/integration/database.spec.ts b/tests/integration/database.spec.ts
index d6d38b3..74f699d 100644
--- a/tests/integration/database.spec.ts
+++ b/tests/integration/database.spec.ts
@@ -200,6 +200,70 @@ describe("database authority constraints", () => {
     expect(message.seq).toBe(1n);
   });
 
+  it("rejects duplicate message client ids within a conversation", async () => {
+    const author = await createAccount("message-client-id");
+    const bottle = await createBottle(author.id, "message-client-id");
+    const conversation = await prisma.conversation.create({
+      data: { sourceBottleId: bottle.id },
+    });
+
+    await expect(
+      prisma.message.create({
+        data: {
+          conversationId: conversation.id,
+          senderId: author.id,
+          clientMsgId: "duplicate-client-id",
+          seq: 1n,
+          contentText: "first",
+        },
+      }),
+    ).resolves.toMatchObject({ clientMsgId: "duplicate-client-id", seq: 1n });
+
+    await expectUniqueViolation(
+      prisma.message.create({
+        data: {
+          conversationId: conversation.id,
+          senderId: author.id,
+          clientMsgId: "duplicate-client-id",
+          seq: 2n,
+          contentText: "second",
+        },
+      }),
+    );
+  });
+
+  it("rejects duplicate message sequences within a conversation", async () => {
+    const author = await createAccount("message-seq");
+    const bottle = await createBottle(author.id, "message-seq");
+    const conversation = await prisma.conversation.create({
+      data: { sourceBottleId: bottle.id },
+    });
+
+    await expect(
+      prisma.message.create({
+        data: {
+          conversationId: conversation.id,
+          senderId: author.id,
+          clientMsgId: "first-client-id",
+          seq: 1n,
+          contentText: "first",
+        },
+      }),
+    ).resolves.toMatchObject({ clientMsgId: "first-client-id", seq: 1n });
+
+    await expectUniqueViolation(
+      prisma.message.create({
+        data: {
+          conversationId: conversation.id,
+          senderId: author.id,
+          clientMsgId: "second-client-id",
+          seq: 1n,
+          contentText: "second",
+        },
+      }),
+    );
+  });
+
   it("rejects self-blocks", async () => {
     const account = await createAccount("self-block");
     await expectConstraintViolation(