diff --git a/CHANGES/5343.bugfix b/CHANGES/5343.bugfix
new file mode 100644
index 00000000000..4e33071ea94
--- /dev/null
+++ b/CHANGES/5343.bugfix
@@ -0,0 +1 @@
+Fixed StreamResponse.prepared to return True after EOF is sent -- by :user:`arthurdarcet`.
diff --git a/aiohttp/web_response.py b/aiohttp/web_response.py
index a0ee89d6706..238c31277bc 100644
--- a/aiohttp/web_response.py
+++ b/aiohttp/web_response.py
@@ -121,7 +121,7 @@ def __init__(
 
     @property
     def prepared(self) -> bool:
-        return self._payload_writer is not None
+        return self._eof_sent or self._payload_writer is not None
 
     @property
     def task(self) -> "Optional[asyncio.Task[None]]":
diff --git a/tests/test_web_response.py b/tests/test_web_response.py
index f90eb4b1153..d1226f27763 100644
--- a/tests/test_web_response.py
+++ b/tests/test_web_response.py
@@ -734,11 +734,8 @@ async def test___repr___after_eof() -> None:
     resp = StreamResponse()
     await resp.prepare(make_request("GET", "/"))
 
-    assert resp.prepared
-
     await resp.write(b"data")
     await resp.write_eof()
-    assert not resp.prepared
     resp_repr = repr(resp)
     assert resp_repr == "<StreamResponse OK eof>"
 
@@ -1110,14 +1107,22 @@ def test_content_type_with_set_body() -> None:
     assert resp.content_type == "application/octet-stream"
 
 
-def test_started_when_not_started() -> None:
+def test_prepared_when_not_started() -> None:
     resp = StreamResponse()
     assert not resp.prepared
 
 
-async def test_started_when_started() -> None:
+async def test_prepared_when_started() -> None:
+    resp = StreamResponse()
+    await resp.prepare(make_request("GET", "/"))
+    assert resp.prepared
+
+
+async def test_prepared_after_eof() -> None:
     resp = StreamResponse()
     await resp.prepare(make_request("GET", "/"))
+    await resp.write(b"data")
+    await resp.write_eof()
     assert resp.prepared