diff --git a/lms/djangoapps/instructor/tests/test_tools.py b/lms/djangoapps/instructor/tests/test_tools.py
index b7c539eb0b..722b57a81c 100644
--- a/lms/djangoapps/instructor/tests/test_tools.py
+++ b/lms/djangoapps/instructor/tests/test_tools.py
@@ -199,11 +199,18 @@ class TestSetDueDateExtension(ModuleStoreTestCase):
 
     def test_set_due_date_extension(self):
         extended = datetime.datetime(2013, 12, 25, 0, 0, tzinfo=utc)
-        tools.set_due_date_extension(self.course, self.week1, self.user,
-                                     extended)
+        tools.set_due_date_extension(self.course, self.week1, self.user, extended)
         self.assertEqual(self.extended_due(self.week1), extended)
         self.assertEqual(self.extended_due(self.homework), extended)
 
+    def test_set_due_date_extension_create_studentmodule(self):
+        extended = datetime.datetime(2013, 12, 25, 0, 0, tzinfo=utc)
+        user = UserFactory.create()  # No student modules for this user
+        tools.set_due_date_extension(self.course, self.week1, user, extended)
+        extended_due = functools.partial(get_extended_due, self.course, student=user)
+        self.assertEqual(extended_due(self.week1), extended)
+        self.assertEqual(extended_due(self.homework), extended)
+
     def test_reset_due_date_extension(self):
         tools.set_due_date_extension(self.course, self.week1, self.user, None)
         self.assertEqual(self.extended_due(self.week1), None)
diff --git a/lms/djangoapps/instructor/views/tools.py b/lms/djangoapps/instructor/views/tools.py
index 4b6a621b97..d195db7a4c 100644
--- a/lms/djangoapps/instructor/views/tools.py
+++ b/lms/djangoapps/instructor/views/tools.py
@@ -173,13 +173,30 @@ def set_due_date_extension(course, unit, student, due_date):
                 course_id=course.id,
                 module_state_key=node.location
             )
-
             state = json.loads(student_module.state)
-            state['extended_due'] = DATE_FIELD.to_json(due_date)
-            student_module.state = json.dumps(state)
-            student_module.save()
+
         except StudentModule.DoesNotExist:
-            pass
+            # Normally, a StudentModule is created as a side effect of assigning
+            # a value to a property in an XModule or XBlock which has a scope
+            # of 'Scope.user_state'.  Here, we want to alter user state but
+            # can't use the standard XModule/XBlock machinery to do so, because
+            # it fails to take into account that the state being altered might
+            # belong to a student other than the one currently logged in.  As a
+            # result, in our work around, we need to detect whether the
+            # StudentModule has been created for the given student on the given
+            # unit and create it if it is missing, so we can use it to store
+            # the extended due date.
+            student_module = StudentModule.objects.create(
+                student_id=student.id,
+                course_id=course.id,
+                module_state_key=node.location,
+                module_type=node.category
+            )
+            state = {}
+
+        state['extended_due'] = DATE_FIELD.to_json(due_date)
+        student_module.state = json.dumps(state)
+        student_module.save()
 
         for child in node.get_children():
             set_due_date(child)