diff --git a/playwright/_impl/_network.py b/playwright/_impl/_network.py
index 3e5b8fe89..616cf3242 100644
--- a/playwright/_impl/_network.py
+++ b/playwright/_impl/_network.py
@@ -1047,7 +1047,7 @@ def get(self, name: str) -> Optional[str]:
         return separator.join(values)
 
     def get_all(self, name: str) -> List[str]:
-        return list(self._headers_map[name.lower()].keys())
+        return list(self._headers_map.get(name.lower(), {}).keys())
 
     def headers(self) -> Dict[str, str]:
         result = {}
diff --git a/tests/async/test_network.py b/tests/async/test_network.py
index e88b24c24..6c5cdfc60 100644
--- a/tests/async/test_network.py
+++ b/tests/async/test_network.py
@@ -371,6 +371,28 @@ async def test_response_headers_should_work(page: Page, server: Server) -> None:
     assert (await response.all_headers())["foo"] == "bar"
 
 
+async def test_header_value_of_missing_header_should_not_add_it_to_all_headers(
+    page: Page, server: Server
+) -> None:
+    server.set_route("/empty.html", lambda r: (r.setHeader("foo", "bar"), r.finish()))
+
+    response = await page.goto(server.EMPTY_PAGE)
+    assert response
+    assert await response.header_value("x-missing") is None
+    assert await response.header_values("x-other") == []
+    headers = await response.all_headers()
+    assert "x-missing" not in headers
+    assert "x-other" not in headers
+    assert headers["foo"] == "bar"
+
+    request = response.request
+    assert await request.header_value("x-missing") is None
+    assert await request.header_value("x-other") is None
+    request_headers = await request.all_headers()
+    assert "x-missing" not in request_headers
+    assert "x-other" not in request_headers
+
+
 async def test_request_post_data_should_work(page: Page, server: Server) -> None:
     await page.goto(server.EMPTY_PAGE)
     server.set_route("/post", lambda r: r.finish())
diff --git a/tests/sync/test_network.py b/tests/sync/test_network.py
index 8c196affb..b12daa0d8 100644
--- a/tests/sync/test_network.py
+++ b/tests/sync/test_network.py
@@ -114,3 +114,25 @@ def test_should_report_service_worker_request(page: Page, server: Server) -> Non
     ) as request_info:
         page.evaluate("() => fetch('/example.txt')")
     assert request_info.value.service_worker == worker_info.value
+
+
+def test_header_value_of_missing_header_should_not_add_it_to_all_headers(
+    page: Page, server: Server
+) -> None:
+    server.set_route("/empty.html", lambda r: (r.setHeader("foo", "bar"), r.finish()))
+
+    response = page.goto(server.EMPTY_PAGE)
+    assert response
+    assert response.header_value("x-missing") is None
+    assert response.header_values("x-other") == []
+    headers = response.all_headers()
+    assert "x-missing" not in headers
+    assert "x-other" not in headers
+    assert headers["foo"] == "bar"
+
+    request = response.request
+    assert request.header_value("x-missing") is None
+    assert request.header_value("x-other") is None
+    request_headers = request.all_headers()
+    assert "x-missing" not in request_headers
+    assert "x-other" not in request_headers