diff --git a/src/debugpy/server/api.py b/src/debugpy/server/api.py
index a1de5874..cdd3d3ef 100644
--- a/src/debugpy/server/api.py
+++ b/src/debugpy/server/api.py
@@ -156,7 +156,8 @@ def listen(address, settrace_kwargs, in_process_debug_adapter=False):
             block_until_connected=False,
             **settrace_kwargs
         )
-        return
+        listen.called = True
+        return host, port
 
     import subprocess
 
diff --git a/tests/debugpy/test_api.py b/tests/debugpy/test_api.py
new file mode 100644
index 00000000..768edb99
--- /dev/null
+++ b/tests/debugpy/test_api.py
@@ -0,0 +1,18 @@
+import pytest
+
+import debugpy.server.api as _api
+
+
+@pytest.fixture
+def no_settrace(monkeypatch):
+    # Avoid actually starting pydevd; we only care about listen()'s return value.
+    monkeypatch.setattr(_api, "_settrace", lambda **kwargs: None)
+    monkeypatch.setattr(_api.listen, "called", False)
+
+
+def test_listen_in_process_returns_endpoint(no_settrace):
+    # Regression test for #1656: listen(..., in_process_debug_adapter=True) used
+    # to return None, unlike the out-of-process path which returns (host, port).
+    endpoint = _api.listen(("127.0.0.1", 5678), in_process_debug_adapter=True)
+    assert endpoint == ("127.0.0.1", 5678)
+    assert _api.listen.called is True