diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2c2df7f8d0..fcbf20578e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 This changelog format was introduced in NAV 5.4.0. Older changelogs can be
 found in the [HISTORY](HISTORY) file.
 
+## [Unreleased]
+
+## Fixed
+
+- Merge two fixes from the 5.4.x stable series that never actually made it into the 5.5 series:
+  - Metric values of 0.0 are evaluated correctly by threshold rules [#2447](https://github.com/Uninett/nav/issues/2447)
+  - Validate maintenance calendar input form to avoid e-mail spam from bots scanning for vulnerabilities [#2420](https://github.com/Uninett/nav/issues/2420)
+
+
 ## [5.5.2] - 2022-11-10
 
 ### Fixed
diff --git a/python/nav/web/maintenance/forms.py b/python/nav/web/maintenance/forms.py
index 6b041165d3..2ef1961ad9 100644
--- a/python/nav/web/maintenance/forms.py
+++ b/python/nav/web/maintenance/forms.py
@@ -13,11 +13,11 @@
 # details.  You should have received a copy of the GNU General Public License
 # along with NAV. If not, see <http://www.gnu.org/licenses/>.
 #
+from datetime import date
 
 from django import forms
 from crispy_forms.helper import FormHelper
 from crispy_forms_foundation.layout import Layout, Row, Column, Field
-
 from nav.models.fields import INFINITY
 
 
@@ -72,3 +72,63 @@ class MaintenanceAddSingleNetbox(forms.Form):
     a custom variable-checker"""
 
     netboxid = forms.IntegerField(required=True)
+
+
+def _get_current_year():
+    return date.today().year
+
+
+def _get_current_month():
+    return date.today().month
+
+
+class MaintenanceCalendarForm(forms.Form):
+    """A form used for displaying a maintenance calendar"""
+
+    year = forms.IntegerField(
+        initial=_get_current_year, required=True, min_value=2000, max_value=2100
+    )
+    month = forms.IntegerField(
+        initial=_get_current_month, required=True, min_value=1, max_value=12
+    )
+
+    @property
+    def cleaned_year(self):
+        """Returns the cleaned year value if valid, current year otherwise"""
+        return self.cleaned_data['year'] if self.is_valid() else _get_current_year()
+
+    @property
+    def cleaned_month(self):
+        """Returns the cleaned month if valid, current month otherwise"""
+        return self.cleaned_data['month'] if self.is_valid() else _get_current_month()
+
+    @property
+    def this_month_start(self):
+        """Returns the first date of the month represented by this form instance"""
+        return date(self.cleaned_year, self.cleaned_month, 1)
+
+    @property
+    def next_month_start(self):
+        """Returns the first date of the month after the one represented by this form
+        instance
+        """
+        year = self.cleaned_year
+        month = self.cleaned_month + 1
+
+        if month > 12:
+            year += 1
+            month = 1
+        return date(year, month, 1)
+
+    @property
+    def previous_month_start(self):
+        """Returns the first date of the month before the one represented by this form
+        instance
+        """
+        year = self.cleaned_year
+        month = self.cleaned_month - 1
+
+        if month < 1:
+            year -= 1
+            month = 12
+        return date(year, month, 1)
diff --git a/python/nav/web/maintenance/views.py b/python/nav/web/maintenance/views.py
index 1b4a02b3c6..01d74adb8f 100644
--- a/python/nav/web/maintenance/views.py
+++ b/python/nav/web/maintenance/views.py
@@ -38,7 +38,7 @@
 from nav.web.maintenance.utils import structure_component_data
 from nav.web.maintenance.utils import task_form_initial, infodict_by_state
 from nav.web.maintenance.utils import MaintenanceCalendar, NAVPATH, TITLE
-from nav.web.maintenance.forms import MaintenanceTaskForm
+from nav.web.maintenance.forms import MaintenanceTaskForm, MaintenanceCalendarForm
 from nav.web.maintenance.forms import MaintenanceAddSingleNetbox
 import nav.maintengine
 
@@ -55,56 +55,41 @@ def redirect_to_calendar(_request):
 def calendar(request, year=None, month=None):
     # If the form was used to get here, redirect to the appropriate page
     if "year" in request.GET and "month" in request.GET:
-        return redirect(
-            "maintenance-calendar",
-            year=request.GET.get("year"),
-            month=request.GET.get("month"),
+        form = MaintenanceCalendarForm(data=request.GET.dict())
+        if form.is_valid():
+            return redirect(
+                "maintenance-calendar",
+                year=request.GET.get("year"),
+                month=request.GET.get("month"),
+            )
+    elif year and month:
+        form = MaintenanceCalendarForm(
+            data={'year': year, 'month': month},
         )
+    else:
+        form = MaintenanceCalendarForm()
 
-    heading = "Maintenance schedule"
-    try:
-        year = int(year)
-        month = int(month)
-        this_month_start = date(year, month, 1)
-    except (TypeError, ValueError):
-        year = date.today().year
-        month = date.today().month
-        this_month_start = date(year, month, 1)
-
-    next_month = month + 1
-    next_year = year
-    if next_month > 12:
-        next_year = year + 1
-        next_month = 1
-
-    prev_month = month - 1
-    prev_year = year
-    if prev_month < 1:
-        prev_year = year - 1
-        prev_month = 12
-
-    prev_month_start = date(prev_year, prev_month, 1)
-    next_month_start = date(next_year, next_month, 1)
     tasks = (
         MaintenanceTask.objects.filter(
-            start_time__lt=next_month_start, end_time__gt=this_month_start
+            start_time__lt=form.next_month_start, end_time__gt=form.this_month_start
         )
         .exclude(state=MaintenanceTask.STATE_CANCELED)
         .order_by('start_time')
     )
-    cal = MaintenanceCalendar(tasks).formatmonth(year, month)
+    cal = MaintenanceCalendar(tasks).formatmonth(form.cleaned_year, form.cleaned_month)
     return render(
         request,
         'maintenance/calendar.html',
         {
             'active': {'calendar': True},
+            'calendarform': form,
             'navpath': NAVPATH,
             'title': TITLE,
-            'heading': heading,
+            'heading': "Maintenance schedule",
             'calendar': mark_safe(cal),
-            'prev_month': prev_month_start,
-            'this_month': this_month_start,
-            'next_month': next_month_start,
+            'prev_month': form.previous_month_start,
+            'this_month': form.this_month_start,
+            'next_month': form.next_month_start,
             'curr_month': datetime.today(),
         },
     )
diff --git a/python/nav/web/templates/maintenance/calendar.html b/python/nav/web/templates/maintenance/calendar.html
index 713a27fc0e..a1f51f289b 100644
--- a/python/nav/web/templates/maintenance/calendar.html
+++ b/python/nav/web/templates/maintenance/calendar.html
@@ -11,8 +11,18 @@
       </a>
 
       <form action="{% url 'maintenance-calendar' %}" method="get" class="inline-form">
-        <input type="text" name="year" value="{{ this_month.year }}" size="4" maxlength="4"/>
-        <input type="text" name="month" value="{{ this_month.month }}" size="2" maxlength="2"/>
+          <input type="number" name="year"
+                 value="{{ calendarform.year.value }}"
+                 min="{{ calendarform.year.field.min_value }}"
+                 max="{{ calendarform.year.field.max_value }}"
+                 required
+                 id="id_year"/>
+          <input type="number" name="month"
+                 value="{{ calendarform.month.value }}"
+                 min="{{ calendarform.month.field.min_value }}"
+                 max="{{ calendarform.month.field.max_value }}"
+                 required
+                 id="id_month"/>
         <button type="submit" class="small secondary"><i class="fa fa-search"></i></button>
       </form>
 
@@ -26,9 +36,11 @@
         <i class="fa fa-step-forward fa-lg" title="Next month"></i>
       </a>
     </div>
-
-    {{ calendar }}
+      {% if calendarform.errors %}
+          {{ calendarform.errors }}
+      {% else %}
+          {{ calendar }}
+      {% endif %}
   </div>
 
-{% endblock %}
-
+{% endblock %}
\ No newline at end of file
diff --git a/tests/integration/web/maintenance/__init__.py b/tests/integration/web/maintenance/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/integration/web/maintenance/views_test.py b/tests/integration/web/maintenance/views_test.py
new file mode 100644
index 0000000000..78b1dc91ea
--- /dev/null
+++ b/tests/integration/web/maintenance/views_test.py
@@ -0,0 +1,25 @@
+#
+# Copyright (C) 2022 Sikt
+#
+# This file is part of Network Administration Visualized (NAV).
+#
+# NAV is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License version 3 as published by
+# the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+# more details.  You should have received a copy of the GNU General Public
+# License along with NAV. If not, see <http://www.gnu.org/licenses/>.
+#
+
+
+class TestMaintenanceCalendarView:
+    def test_calendar_renders_when_no_arguments_given(self, client):
+        response = client.get('/maintenance/', follow=True)
+        assert response.status_code == 200
+
+    def test_calendar_still_renders_when_invalid_arguments_given(self, client):
+        response = client.get('/maintenance/?year=invalid&month=invalid', follow=True)
+        assert response.status_code == 200
diff --git a/tests/unittests/web/maintenance/__init__.py b/tests/unittests/web/maintenance/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/unittests/web/maintenance/forms_test.py b/tests/unittests/web/maintenance/forms_test.py
new file mode 100644
index 0000000000..9910562d2b
--- /dev/null
+++ b/tests/unittests/web/maintenance/forms_test.py
@@ -0,0 +1,64 @@
+#
+# Copyright (C) 2022 Sikt
+#
+# This file is part of Network Administration Visualized (NAV).
+#
+# NAV is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License version 3 as published by
+# the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+# more details.  You should have received a copy of the GNU General Public
+# License along with NAV. If not, see <http://www.gnu.org/licenses/>.
+#
+from datetime import date
+
+import pytest
+
+from nav.web.maintenance.forms import MaintenanceCalendarForm
+
+
+class TestMaintenanceCalendarForm:
+    def test_cleaned_year_returns_integer(self, valid_form):
+        assert valid_form.cleaned_year == 2022
+
+    def test_cleaned_month_returns_integer(self, valid_form):
+        assert valid_form.cleaned_month == 7
+
+    def test_this_month_start_returns_the_first_day_of_the_month(self, valid_form):
+        assert valid_form.this_month_start == date(2022, 7, 1)
+
+    def test_next_month_start_returns_the_first_day_of_the_next_month(self, valid_form):
+        assert valid_form.next_month_start == date(2022, 8, 1)
+
+    def test_previous_month_start_returns_the_first_day_of_the_previous_month(
+        self, valid_form
+    ):
+        assert valid_form.previous_month_start == date(2022, 6, 1)
+
+    def test_when_month_is_december_next_month_start_returns_january(
+        self, december_form
+    ):
+        assert december_form.next_month_start == date(2023, 1, 1)
+
+    def test_when_month_is_january_previous_month_start_returns_december(
+        self, january_form
+    ):
+        assert january_form.previous_month_start == date(2021, 12, 1)
+
+
+@pytest.fixture
+def valid_form() -> MaintenanceCalendarForm:
+    return MaintenanceCalendarForm(data={'year': '2022', 'month': '7'})
+
+
+@pytest.fixture
+def december_form() -> MaintenanceCalendarForm:
+    return MaintenanceCalendarForm(data={'year': '2022', 'month': '12'})
+
+
+@pytest.fixture
+def january_form() -> MaintenanceCalendarForm:
+    return MaintenanceCalendarForm(data={'year': '2022', 'month': '1'})