From 4ddb4e94c67a4d8712fc656bcd9882b8f7e2b2f4 Mon Sep 17 00:00:00 2001
From: Mihai Cara <mihail.cara@gmail.com>
Date: Wed, 3 Jun 2020 16:31:22 -0400
Subject: [PATCH] Do not issue datfix warning when MJDREF has default value

---
 CHANGES.rst        | 2 ++ (removed for rebase)
 astropy/wcs/wcs.py | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/astropy/wcs/wcs.py b/astropy/wcs/wcs.py
index 7f5f79bbc95..aa3a4d77951 100644
--- a/astropy/wcs/wcs.py
+++ b/astropy/wcs/wcs.py
@@ -681,6 +681,9 @@ def fix(self, translate_units='', naxis=None):
             fixes = self.wcs.fix(translate_units, naxis)
             for key, val in fixes.items():
                 if val != "No change":
+                    if (key == 'datfix' and '1858-11-17' in val and
+                            not np.count_nonzero(self.wcs.mjdref)):
+                        continue
                     warnings.warn(
                         ("'{0}' made the change '{1}'.").
                         format(key, val),