From 03a49813074c84665c9ea611c56bb0059f434227 Mon Sep 17 00:00:00 2001
From: Patrick Hoefler <61934744+phofl@users.noreply.github.com>
Date: Mon, 23 Oct 2023 20:08:35 +0200
Subject: [PATCH] BUG: indexing raises for ea into numpy series (#55633)

---
 doc/source/whatsnew/v2.2.0.rst              |  2 +-
 pandas/core/dtypes/cast.py                  |  3 ++-
 pandas/tests/frame/indexing/test_setitem.py | 11 +++++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
index 9b3cc92437c12..a3457d25493c1 100644
--- a/doc/source/whatsnew/v2.2.0.rst
+++ b/doc/source/whatsnew/v2.2.0.rst
@@ -345,9 +345,9 @@ Interval
 
 Indexing
 ^^^^^^^^
+- Bug in :meth:`DataFrame.loc` when setting :class:`Series` with extension dtype into NumPy dtype (:issue:`55604`)
 - Bug in :meth:`Index.difference` not returning a unique set of values when ``other`` is empty or ``other`` is considered non-comparable (:issue:`55113`)
 - Bug in setting :class:`Categorical` values into a :class:`DataFrame` with numpy dtypes raising ``RecursionError`` (:issue:`52927`)
--
 
 Missing
 ^^^^^^^
diff --git a/pandas/core/dtypes/cast.py b/pandas/core/dtypes/cast.py
index 28e83fd70519c..27625db766862 100644
--- a/pandas/core/dtypes/cast.py
+++ b/pandas/core/dtypes/cast.py
@@ -1816,7 +1816,8 @@ def np_can_hold_element(dtype: np.dtype, element: Any) -> Any:
             if not isinstance(tipo, np.dtype):
                 # i.e. nullable IntegerDtype; we can put this into an ndarray
                 #  losslessly iff it has no NAs
-                if element._hasna:
+                arr = element._values if isinstance(element, ABCSeries) else element
+                if arr._hasna:
                     raise LossySetitemError
                 return element
 
diff --git a/pandas/tests/frame/indexing/test_setitem.py b/pandas/tests/frame/indexing/test_setitem.py
index ccc1249088f9a..7db8f51afe291 100644
--- a/pandas/tests/frame/indexing/test_setitem.py
+++ b/pandas/tests/frame/indexing/test_setitem.py
@@ -761,6 +761,17 @@ def test_setitem_frame_midx_columns(self):
         df[col_name] = df[[col_name]]
         tm.assert_frame_equal(df, expected)
 
+    def test_loc_setitem_ea_dtype(self):
+        # GH#55604
+        df = DataFrame({"a": np.array([10], dtype="i8")})
+        df.loc[:, "a"] = Series([11], dtype="Int64")
+        expected = DataFrame({"a": np.array([11], dtype="i8")})
+        tm.assert_frame_equal(df, expected)
+
+        df = DataFrame({"a": np.array([10], dtype="i8")})
+        df.iloc[:, 0] = Series([11], dtype="Int64")
+        tm.assert_frame_equal(df, expected)
+
 
 class TestSetitemTZAwareValues:
     @pytest.fixture