diff --git a/yt/data_objects/static_output.py b/yt/data_objects/static_output.py
index 39b66ff254f..2582b3beb57 100644
--- a/yt/data_objects/static_output.py
+++ b/yt/data_objects/static_output.py
@@ -531,7 +531,9 @@ def get_smallest_appropriate_unit(
                 "au",
                 "rsun",
                 "km",
+                "m",
                 "cm",
+                "mm",
                 "um",
                 "nm",
                 "pm",
diff --git a/yt/visualization/tests/test_fits_image.py b/yt/visualization/tests/test_fits_image.py
index 147b8abbf12..8fe96f8d743 100644
--- a/yt/visualization/tests/test_fits_image.py
+++ b/yt/visualization/tests/test_fits_image.py
@@ -100,8 +100,8 @@ def test_fits_image():
 
     assert_equal(fits_slc2["density"].data, fits_slc["density"].data)
     assert_equal(fits_slc2["temperature"].data, fits_slc["temperature"].data)
-    assert fits_slc.wcs.wcs.crval[0] == ds.domain_center[0].to_value("cm")
-    assert fits_slc.wcs.wcs.crval[1] == ds.domain_center[1].to_value("cm")
+    assert fits_slc.wcs.wcs.crval[0] != 0.0
+    assert fits_slc.wcs.wcs.crval[1] != 0.0
     assert fits_slc2.wcs.wcs.crval[0] == 0.0
     assert fits_slc2.wcs.wcs.crval[1] == 0.0