diff --git a/.flake8 b/.flake8
index d967a505b..b87fef8b2 100644
--- a/.flake8
+++ b/.flake8
@@ -11,6 +11,7 @@ exclude = .*,__pycache__,resources.py
 #       (for pytest's __tracebackhide__)
 # F401: Unused import
 # N802: function name should be lowercase
+# N806: variable in function should be lowercase
 # P101: format string does contain unindexed parameters
 # P102: docstring does contain unindexed parameters
 # P103: other string does contain unindexed parameters
@@ -27,7 +28,7 @@ exclude = .*,__pycache__,resources.py
 ignore =
     E128,E226,E265,E501,E402,E266,E722,E731,
     F401,
-    N802,
+    N802,N806
     P101,P102,P103,
     D102,D103,D104,D105,D209,D211,D402,D403
 min-version = 3.4.0
diff --git a/qutebrowser/completion/completionwidget.py b/qutebrowser/completion/completionwidget.py
index 9b8d31ad6..68466630a 100644
--- a/qutebrowser/completion/completionwidget.py
+++ b/qutebrowser/completion/completionwidget.py
@@ -290,6 +290,8 @@ class CompletionView(QTreeView):
             self.expand(model.index(i, 0))
 
     def set_pattern(self, pattern):
+        if not self.model():
+            return
         self.pattern = pattern
         with debug.log_time(log.completion, 'Set pattern {}'.format(pattern)):
             self.model().set_pattern(pattern)
diff --git a/tests/helpers/fixtures.py b/tests/helpers/fixtures.py
index e38a3ce49..74c63f251 100644
--- a/tests/helpers/fixtures.py
+++ b/tests/helpers/fixtures.py
@@ -490,6 +490,7 @@ class ModelValidator:
 
     def __init__(self, modeltester):
         modeltester.data_display_may_return_none = True
+        self._model = None
         self._modeltester = modeltester
 
     def set_model(self, model):
diff --git a/tests/unit/browser/test_history.py b/tests/unit/browser/test_history.py
index 0b5e6eb41..5a8425646 100644
--- a/tests/unit/browser/test_history.py
+++ b/tests/unit/browser/test_history.py
@@ -20,7 +20,6 @@
 """Tests for the global page history."""
 
 import logging
-import os
 
 import pytest
 from PyQt5.QtCore import QUrl
diff --git a/tests/unit/completion/test_completionwidget.py b/tests/unit/completion/test_completionwidget.py
index cad45b5c1..207e557a8 100644
--- a/tests/unit/completion/test_completionwidget.py
+++ b/tests/unit/completion/test_completionwidget.py
@@ -89,6 +89,11 @@ def test_set_pattern(completionview):
     model.set_pattern.assert_called_with('foo')
 
 
+def test_set_pattern_no_model(completionview):
+    """Ensure that setting a pattern with no model does not fail."""
+    completionview.set_pattern('foo')
+
+
 def test_maybe_update_geometry(completionview, config_stub, qtbot):
     """Ensure completion is resized only if shrink is True."""
     with qtbot.assertNotEmitted(completionview.update_geometry):
@@ -233,4 +238,4 @@ def test_completion_item_del_no_selection(completionview):
     completionview.set_model(model)
     with pytest.raises(cmdexc.CommandError, match='No item selected!'):
         completionview.completion_item_del()
-    func.assert_not_called()
+    assert not func.called