diff --git a/rich/segment.py b/rich/segment.py
index 34f84b9dc..0f0676876 100644
--- a/rich/segment.py
+++ b/rich/segment.py
@@ -142,12 +142,12 @@ def _split_cells(cls, segment: "Segment", cut: int) -> Tuple["Segment", "Segment
                 )
             if out_by == -1 and cell_size(text[pos]) == 2:
                 return (
-                    _Segment(before[:pos] + " ", style, control),
+                    _Segment(text[:pos] + " ", style, control),
                     _Segment(" " + text[pos + 1 :], style, control),
                 )
-            if out_by == +1 and cell_size(text[pos]) == 2:
+            if out_by == +1 and cell_size(text[pos - 1]) == 2:
                 return (
-                    _Segment(before[: pos - 1] + " ", style, control),
+                    _Segment(text[: pos - 1] + " ", style, control),
                     _Segment(" " + text[pos:], style, control),
                 )
             if cell_pos < cut:
diff --git a/tests/test_segment.py b/tests/test_segment.py
index 4bdb01453..3673f129b 100644
--- a/tests/test_segment.py
+++ b/tests/test_segment.py
@@ -285,19 +285,27 @@ def test_split_cells_emoji(text, split, result):
     assert Segment(text).split_cells(split) == result
 
 
-def test_split_cells_mixed() -> None:
-    """Check that split cells splits on cell positions."""
-    # Caused https://github.com/Textualize/textual/issues/4996 in Textual
-    tests = [
+@pytest.mark.parametrize(
+    "segment",
+    [
         Segment("早乙女リリエル (CV: 徳井青）"),
-        Segment("メイド・イン・きゅんクチュアリ☆"),
+        Segment("メイド・イン・きゅんクチュアリ☆    "),
         Segment("TVアニメ「メルクストーリア -無気力少年と瓶の中の少女-」 主題歌CD"),
-    ]
-    for test in tests:
-        for position in range(1, test.cell_length):
-            left, right = Segment.split_cells(test, position)
-            assert cell_len(left.text) == position
-            assert cell_len(right.text) == test.cell_length - position
+        Segment("南無阿弥JKうらめしや?！     "),
+        Segment("メルク (CV: 水瀬いのり)     "),
+    ],
+)
+def test_split_cells_mixed(segment: Segment) -> None:
+    """Check that split cells splits on cell positions."""
+    # Caused https://github.com/Textualize/textual/issues/4996 in Textual
+
+    for position in range(0, segment.cell_length + 1):
+        left, right = Segment.split_cells(segment, position)
+        assert all(
+            cell_len(c) > 0 for c in segment.text
+        )  # Sanity check there aren't any sneaky control codes
+        assert cell_len(left.text) == position
+        assert cell_len(right.text) == segment.cell_length - position
 
 
 def test_split_cells_doubles() -> None: