diff --git a/src/pyqt_reactive/widgets/log_viewer.py b/src/pyqt_reactive/widgets/log_viewer.py
index eba7206..9ba24fd 100644
--- a/src/pyqt_reactive/widgets/log_viewer.py
+++ b/src/pyqt_reactive/widgets/log_viewer.py
@@ -613,7 +613,7 @@ def _precompute_search_matches(self, model) -> None:
         needle = self._search_text if self._case_sensitive else self._search_text.lower()
         for row in range(model.rowCount()):
             index = model.index(row, 0)
-            text = index.data(Qt.DisplayRole)
+            text = index.data(Qt.ItemDataRole.DisplayRole)
             if text:
                 haystack = text if self._case_sensitive else text.lower()
                 if needle in haystack:
@@ -912,7 +912,7 @@ def sizeHint(self, option, index):  # type: ignore[override]
                         width = metrics.horizontalAdvance("M") * max_chars + 8
                 return QSize(width, self._fixed_row_height)
 
-        text = index.data(Qt.DisplayRole)
+        text = index.data(Qt.ItemDataRole.DisplayRole)
         if text is None:
             return super().sizeHint(option, index)
 
diff --git a/tests/test_log_viewer_lifecycle.py b/tests/test_log_viewer_lifecycle.py
index 6342172..29b71ac 100644
--- a/tests/test_log_viewer_lifecycle.py
+++ b/tests/test_log_viewer_lifecycle.py
@@ -4,17 +4,39 @@
 
 from pathlib import Path
 
-from PyQt6.QtCore import qInstallMessageHandler
+from PyQt6.QtCore import Qt, qInstallMessageHandler
+from PyQt6.QtWidgets import QStyleOptionViewItem
 
 from pyqt_reactive.protocols import register_log_discovery_provider
 from pyqt_reactive.utils.log_highlighter import build_log_line_html
 from pyqt_reactive.widgets.log_viewer import (
     LogFileInfo,
     LogFileLoader,
+    LogItemDelegate,
+    LogListModel,
     LogViewerWindow,
 )
 
 
+def test_log_delegate_uses_pyqt6_item_data_role(qtbot) -> None:
+    """Search and sizing must use PyQt6's scoped item-data enum."""
+
+    model = LogListModel()
+    model.append_lines(["alpha", "matching line"])
+    delegate = LogItemDelegate()
+    delegate.set_search_state("matching", case_sensitive=False)
+
+    delegate._precompute_search_matches(model)
+    hint = delegate.sizeHint(QStyleOptionViewItem(), model.index(1, 0))
+
+    assert delegate._search_match_rows == {1}
+    assert (
+        model.data(model.index(1, 0), Qt.ItemDataRole.DisplayRole)
+        == "matching line"
+    )
+    assert hint.isValid()
+
+
 def test_log_line_html_uses_authoritative_highlight_segments() -> None:
     rendered = build_log_line_html(
         "2026-07-29 20:00:00,000 - worker - ERROR - value < 2"