diff --git a/packages/protocol/src/terminal-modified-enter-repro.test.ts b/packages/protocol/src/terminal-modified-enter-repro.test.ts
new file mode 100644
index 0000000000..a88b277208
--- /dev/null
+++ b/packages/protocol/src/terminal-modified-enter-repro.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import { TerminalInputModeTracker } from "./terminal-input-mode";
+import { encodeTerminalKeyInput } from "./terminal-key-input";
+
+describe("Modified Enter negotiation", () => {
+  it("answers a keyboard query split immediately after ESC", () => {
+    const tracker = new TerminalInputModeTracker();
+    tracker.feed("\x1b");
+    expect(tracker.feed("[?u").responses).toEqual(["\x1b[?0u"]);
+  });
+
+  it("recognizes modified Enter after a program enables modifyOtherKeys level 2", () => {
+    const tracker = new TerminalInputModeTracker();
+    tracker.feed("\x1b[>4;2m");
+    expect(tracker.supportsModifiedEnter()).toBe(true);
+  });
+
+  it("distinguishes Shift+Enter from Enter after modifyOtherKeys negotiation", () => {
+    const tracker = new TerminalInputModeTracker();
+    tracker.feed("\x1b[>4;2m");
+    const options = { inputMode: tracker.getState() };
+    expect(encodeTerminalKeyInput({ key: "Enter", shift: true }, options)).toBe("\x1b[27;2;13~");
+    expect(encodeTerminalKeyInput({ key: "Enter" }, options)).toBe("\r");
+  });
+});