diff --git a/esp/esp/program/modules/handlers/studentonsite.py b/esp/esp/program/modules/handlers/studentonsite.py
index 558c9da636..b00575c2a5 100644
--- a/esp/esp/program/modules/handlers/studentonsite.py
+++ b/esp/esp/program/modules/handlers/studentonsite.py
@@ -91,8 +91,11 @@ def onsitedetails(self, request, tl, one, two, module, extra, prog):
         user = request.user
         context['webapp_page'] = 'schedule'
         if extra:
-            secid = extra
-            sections = ClassSection.objects.filter(id = secid)
+            try:
+                sections = ClassSection.objects.filter(id = int(extra))
+            except ValueError:
+                #   Not a number, so treat it like a section that doesn't exist
+                sections = ClassSection.objects.none()
             if len(sections) == 1:
                 section = sections[0]
                 if StudentRegistration.valid_objects().filter(section=section, user=user, relationship__name="Enrolled"):
diff --git a/esp/esp/program/modules/tests/test_studentonsite_details.py b/esp/esp/program/modules/tests/test_studentonsite_details.py
new file mode 100644
index 0000000000..6496942f2b
--- /dev/null
+++ b/esp/esp/program/modules/tests/test_studentonsite_details.py
@@ -0,0 +1,58 @@
+from esp.program.models import ProgramModule, StudentRegistration
+from esp.program.tests import ProgramFrameworkTest
+
+# ProgramFrameworkTest enables every module by default, and some required ones
+# (the lottery, the medical form) take over the page for a student who hasn't
+# completed them. Only enable what the onsite pages need, so these tests reach
+# the onsite view itself.
+ONSITE_MODULES = ['StudentOnsite', 'StudentClassRegModule', 'StudentRegCore']
+
+
+class StudentOnsiteDetailsSectionIdTest(ProgramFrameworkTest):
+
+    def setUp(self):
+        super().setUp(
+            num_students=1, num_teachers=1, classes_per_teacher=1,
+            modules=ProgramModule.objects.filter(handler__in=ONSITE_MODULES),
+        )
+        self.add_student_profiles()
+        self.schedule_randomly()
+        self.student = self.students[0]
+        self.section = self.program.sections().first()
+        self.schedule_url = self.program.get_learn_url() + 'studentonsite'
+        self.assertTrue(self.client.login(username=self.student.username, password='password'))
+
+    def details(self, extra=None):
+        url = self.program.get_learn_url() + 'onsitedetails'
+        if extra is not None:
+            url += '/' + extra
+        return self.client.get(url)
+
+    def assert_redirects_to_schedule(self, response, msg=''):
+        self.assertRedirects(response, self.schedule_url, fetch_redirect_response=False, msg_prefix=msg)
+
+    def test_enrolled_section_shows_section_info(self):
+        self.section.preregister_student(self.student, fast_force_create=True)
+        response = self.details(str(self.section.id))
+        self.assertEqual(response.status_code, 200)
+        self.assertTemplateUsed(response, 'program/modules/studentonsite/sectioninfo.html')
+        self.assertEqual(response.context['section'], self.section)
+
+    def test_section_student_is_not_enrolled_in_redirects(self):
+        self.assert_redirects_to_schedule(self.details(str(self.section.id)))
+
+    def test_missing_section_id_redirects(self):
+        self.assert_redirects_to_schedule(self.details())
+
+    def test_unknown_numeric_section_id_redirects(self):
+        for extra in ('999999', '0', '-1'):
+            self.assert_redirects_to_schedule(self.details(extra), 'extra=%r: ' % extra)
+
+    def test_non_numeric_section_id_redirects(self):
+        # Even a student who is enrolled in a section must not be shown it
+        self.section.preregister_student(self.student, fast_force_create=True)
+        for extra in ('abc', '12abc', '0x10', '1e5'):
+            self.assert_redirects_to_schedule(self.details(extra), 'extra=%r: ' % extra)
+
+    def test_out_of_range_section_id_redirects(self):
+        self.assert_redirects_to_schedule(self.details('99999999999999999999'))