diff --git a/lms/djangoapps/instructor/tests/test_tools.py b/lms/djangoapps/instructor/tests/test_tools.py
index aa216625a7..35ca654255 100644
--- a/lms/djangoapps/instructor/tests/test_tools.py
+++ b/lms/djangoapps/instructor/tests/test_tools.py
@@ -62,6 +62,27 @@ class TestHandleDashboardError(unittest.TestCase):
         self.assertEqual(view(None, None), "Oh yes!")
 
 
+class TestRequireStudentIdentifier(unittest.TestCase):
+    """
+    Test require_student_from_identifier()
+    """
+    def setUp(self):
+        """
+        Fixtures
+        """
+        self.student = UserFactory.create()
+
+    def test_valid_student_id(self):
+        self.assertEqual(
+            self.student,
+            tools.require_student_from_identifier(self.student.username)
+        )
+
+    def test_invalid_student_id(self):
+        with self.assertRaises(tools.DashboardError):
+            tools.require_student_from_identifier("invalid")
+
+
 class TestParseDatetime(unittest.TestCase):
     """
     Test date parsing.
diff --git a/lms/djangoapps/instructor/views/api.py b/lms/djangoapps/instructor/views/api.py
index 72990cbea4..18e08b9138 100644
--- a/lms/djangoapps/instructor/views/api.py
+++ b/lms/djangoapps/instructor/views/api.py
@@ -66,6 +66,7 @@ from .tools import (
     dump_module_extensions,
     find_unit,
     get_student_from_identifier,
+    require_student_from_identifier,
     handle_dashboard_error,
     parse_datetime,
     set_due_date_extension,
@@ -1392,7 +1393,7 @@ def change_due_date(request, course_id):
     Grants a due date extension to a student for a particular unit.
     """
     course = get_course_by_id(SlashSeparatedCourseKey.from_deprecated_string(course_id))
-    student = get_student_from_identifier(request.GET.get('student'))
+    student = require_student_from_identifier(request.GET.get('student'))
     unit = find_unit(course, request.GET.get('url'))
     due_date = parse_datetime(request.GET.get('due_datetime'))
     set_due_date_extension(course, unit, student, due_date)
@@ -1413,7 +1414,7 @@ def reset_due_date(request, course_id):
     Rescinds a due date extension for a student on a particular unit.
     """
     course = get_course_by_id(SlashSeparatedCourseKey.from_deprecated_string(course_id))
-    student = get_student_from_identifier(request.GET.get('student'))
+    student = require_student_from_identifier(request.GET.get('student'))
     unit = find_unit(course, request.GET.get('url'))
     set_due_date_extension(course, unit, student, None)
     if not getattr(unit, "due", None):
@@ -1453,7 +1454,7 @@ def show_student_extensions(request, course_id):
     Shows all of the due date extensions granted to a particular student in a
     particular course.
     """
-    student = get_student_from_identifier(request.GET.get('student'))
+    student = require_student_from_identifier(request.GET.get('student'))
     course = get_course_by_id(SlashSeparatedCourseKey.from_deprecated_string(course_id))
     return JsonResponse(dump_student_extensions(course, student))
 
diff --git a/lms/djangoapps/instructor/views/tools.py b/lms/djangoapps/instructor/views/tools.py
index 44919ca064..302b0755fb 100644
--- a/lms/djangoapps/instructor/views/tools.py
+++ b/lms/djangoapps/instructor/views/tools.py
@@ -90,6 +90,21 @@ def get_student_from_identifier(unique_student_identifier):
     return student
 
 
+def require_student_from_identifier(unique_student_identifier):
+    """
+    Same as get_student_from_identifier() but will raise a DashboardError if
+    the student does not exist.
+    """
+    try:
+        return get_student_from_identifier(unique_student_identifier)
+    except User.DoesNotExist:
+        raise DashboardError(
+            _("Could not find student matching identifier: {student_identifier}").format(
+                student_identifier=unique_student_identifier
+            )
+        )
+
+
 def parse_datetime(datestr):
     """
     Convert user input date string into an instance of `datetime.datetime` in