diff --git a/openedx/core/djangoapps/programs/tests/test_utils.py b/openedx/core/djangoapps/programs/tests/test_utils.py
index c49ff9c03e..9407f83fd9 100644
--- a/openedx/core/djangoapps/programs/tests/test_utils.py
+++ b/openedx/core/djangoapps/programs/tests/test_utils.py
@@ -820,6 +820,22 @@ class TestSupplementProgramData(ProgramsApiConfigMixin, ModuleStoreTestCase):
             enrollment_open_date=enrollment_open_date,
         )
 
+    def test_no_enrollment_start_date(self):
+        """Verify that a closed course with no explicit enrollment start date doesn't cause an error.
+
+        Regression test for ECOM-4973.
+        """
+        self.course.enrollment_end = timezone.now() - datetime.timedelta(days=1)
+        self.course = self.update_course(self.course, self.user.id)  # pylint: disable=no-member
+
+        data = utils.supplement_program_data(self.program, self.user)
+
+        self._assert_supplemented(
+            data,
+            is_enrollment_open=False,
+            enrollment_open_date=strftime_localized(utils.DEFAULT_ENROLLMENT_START_DATE, 'SHORT_DATE'),
+        )
+
     @ddt.data(True, False)
     @mock.patch(UTILS_MODULE + '.certificate_api.certificate_downloadable_status')
     @mock.patch(CERTIFICATES_API_MODULE + '.has_html_certificates_enabled')
diff --git a/openedx/core/djangoapps/programs/utils.py b/openedx/core/djangoapps/programs/utils.py
index 3f9b8d9a7a..48b51dfdcb 100644
--- a/openedx/core/djangoapps/programs/utils.py
+++ b/openedx/core/djangoapps/programs/utils.py
@@ -25,6 +25,9 @@ from xmodule.course_metadata_utils import DEFAULT_START_DATE
 
 log = logging.getLogger(__name__)
 
+# The datetime module's strftime() methods require a year >= 1900.
+DEFAULT_ENROLLMENT_START_DATE = datetime.datetime(1900, 1, 1, tzinfo=pytz.UTC)
+
 
 def get_programs(user, program_id=None):
     """Given a user, get programs from the Programs service.
@@ -356,7 +359,7 @@ def supplement_program_data(program_data, user):
 
             is_enrolled = CourseEnrollment.is_enrolled(user, course_key)
 
-            enrollment_start = course_overview.enrollment_start or datetime.datetime.min.replace(tzinfo=pytz.UTC)
+            enrollment_start = course_overview.enrollment_start or DEFAULT_ENROLLMENT_START_DATE
             enrollment_end = course_overview.enrollment_end or datetime.datetime.max.replace(tzinfo=pytz.UTC)
             is_enrollment_open = enrollment_start <= timezone.now() < enrollment_end