diff --git a/admin/tests/test_logs_page.py b/admin/tests/test_logs_page.py
index 26c8155d..d371da17 100644
--- a/admin/tests/test_logs_page.py
+++ b/admin/tests/test_logs_page.py
@@ -79,6 +79,16 @@ class LogsPageTests(TestCase):
         self.assertEqual([row[1] for row in values[1:]], ["mallory", "alice"])
         # a message starting with = stays text
         self.assertEqual(sheet.cell(row=2, column=6).data_type, "s")
+        # a bold header that stays in view, with filters over every row
+        self.assertEqual((sheet.freeze_panes, sheet.auto_filter.ref, sheet["A1"].font.b), ("A2", "A1:H3", True))
+
+    def test_the_workbook_is_written_row_by_row(self):
+        # openpyxl's write-only mode: a large download does not keep every cell in memory
+        from openpyxl import Workbook
+
+        with patch("instances.report.Workbook", wraps=Workbook) as book:
+            self.client.get(reverse("admin:logs_export"))
+        book.assert_called_once_with(write_only=True)
         page = self.page(q="alice", failed="1")
         self.assertEqual(page.xpath("//a[contains(@href, 'export')]/@href"),
                          [reverse("admin:logs_export") + "?q=alice&failed=1"])
diff --git a/admin/views.py b/admin/views.py
index a9bb11cb..2b8937e5 100644
--- a/admin/views.py
+++ b/admin/views.py
@@ -306,9 +306,12 @@ def logs_export(request):
     rows, text, failed, _query = _logs(request)
     zone = timezone.get_current_timezone_name()
     header = [f"Date ({zone})", "User", "Host", "VM", "VM UUID", "Message", "Result", "IP"]
-    logs = list(rows[:EXPORT_ROWS + 1])
-    data = [[timezone.localtime(log.date).strftime("%Y-%m-%d %H:%M:%S"), log.user, log.host, log.instance,
-             log.instance_uuid, log.message, str(_result(log.success)), log.ip or ""] for log in logs[:EXPORT_ROWS]]
+    # tuples, not model objects: up to EXPORT_ROWS of them are held at once
+    logs = list(rows.values_list("date", "user", "host", "instance", "instance_uuid", "message", "success", "ip")
+                [:EXPORT_ROWS + 1])
+    data = [[timezone.localtime(date).strftime("%Y-%m-%d %H:%M:%S"), user, host, instance, uuid, message,
+             str(_result(success)), ip or ""]
+            for date, user, host, instance, uuid, message, success, ip in logs[:EXPORT_ROWS]]
     notes = [f"Search: {text}" if text else "Search: none", "Failed only" if failed else "All results",
              f"Rows: {len(data)}", f"Times in {zone}"]
     if len(logs) > EXPORT_ROWS:
diff --git a/instances/report.py b/instances/report.py
index 7a5e12b4..749864c8 100644
--- a/instances/report.py
+++ b/instances/report.py
@@ -3,6 +3,7 @@
 from io import BytesIO
 
 from openpyxl import Workbook
+from openpyxl.cell import WriteOnlyCell
 from openpyxl.cell.cell import ILLEGAL_CHARACTERS_RE
 from openpyxl.styles import Font
 from openpyxl.utils import get_column_letter
@@ -11,31 +12,34 @@ MAX_WIDTH = 60
 
 
 def workbook(title, header, rows, notes_title, notes):
-    """The .xlsx file's bytes. Every text cell stays text: openpyxl would
-    write one starting with "=" as a formula, and the text comes from VM
-    names and guests."""
-    book = Workbook()
-    sheet = book.active
-    sheet.title = title
-    for values in [header, *rows]:
-        # a control character (a name typed at a failed login) cannot be in the file: written as \x01
-        sheet.append([ILLEGAL_CHARACTERS_RE.sub(lambda m: f"\\x{ord(m.group()):02x}", value)
-                      if isinstance(value, str) else value for value in values])
-    for row in sheet.iter_rows():
-        for cell in row:
-            if isinstance(cell.value, str):
-                cell.data_type = "s"
-    for cell in sheet[1]:
-        cell.font = Font(bold=True)
-    sheet.freeze_panes = "A2"
-    sheet.auto_filter.ref = sheet.dimensions
-    for index, column in enumerate(sheet.columns, start=1):
-        width = max(len(str(cell.value or "")) for cell in column) + 2
+    """The .xlsx file's bytes, written row by row (openpyxl's write-only mode:
+    a large download does not hold every cell in memory). Every text cell
+    stays text: openpyxl would write one starting with "=" as a formula, and
+    the text comes from VM names and guests."""
+    book = Workbook(write_only=True)
+    sheet = book.create_sheet(title)
+    # control characters (a name typed at a failed login) cannot be in the file: written as \x01
+    rows = [[ILLEGAL_CHARACTERS_RE.sub(lambda m: f"\\x{ord(m.group()):02x}", value) if isinstance(value, str) else value
+             for value in values] for values in [header, *rows]]
+    for index, column in enumerate(zip(*rows), start=1):
+        width = max(len(str(value or "")) for value in column) + 2
         sheet.column_dimensions[get_column_letter(index)].width = min(width, MAX_WIDTH)
+    sheet.freeze_panes = "A2"
+    for number, values in enumerate(rows):
+        cells = []
+        for value in values:
+            cell = WriteOnlyCell(sheet, value=value)
+            if isinstance(value, str):
+                cell.data_type = "s"
+            if number == 0:
+                cell.font = Font(bold=True)
+            cells.append(cell)
+        sheet.append(cells)
+    sheet.auto_filter.ref = f"A1:{get_column_letter(len(header))}{len(rows)}"
     notes_sheet = book.create_sheet(notes_title)
+    notes_sheet.column_dimensions["A"].width = MAX_WIDTH * 2
     for line in notes:
         notes_sheet.append([line])
-    notes_sheet.column_dimensions["A"].width = MAX_WIDTH * 2
     out = BytesIO()
     book.save(out)
     return out.getvalue()