diff --git a/gwcs/api.py b/gwcs/api.py
index 472357dd..0c32482e 100644
--- a/gwcs/api.py
+++ b/gwcs/api.py
@@ -9,6 +9,8 @@
 from astropy.modeling import separable
 import astropy.units as u
 
+from gwcs import utils
+
 __all__ = ["GWCSAPIMixin"]
 
 
diff --git a/gwcs/tests/test_wcs.py b/gwcs/tests/test_wcs.py
index 06bf4335..bfd5f115 100644
--- a/gwcs/tests/test_wcs.py
+++ b/gwcs/tests/test_wcs.py
@@ -23,7 +23,7 @@
 from gwcs import utils
 from gwcs.wcstools import (wcs_from_fiducial, grid_from_bounding_box, wcs_from_points)
 from gwcs.utils import CoordinateFrameError
-from gwcs.utils import _gwcs_from_hst_fits_wcs
+from gwcs.tests.utils import _gwcs_from_hst_fits_wcs
 from gwcs.tests import data
 from gwcs.examples import gwcs_2d_bad_bounding_box_order
 
@@ -467,7 +467,8 @@ def test_bounding_box_eval():
     Tests evaluation with and without respecting the bounding_box.
     """
     trans3 = models.Shift(10) & models.Scale(2) & models.Shift(-1)
-    pipeline = [('detector', trans3), ('sky', None)]
+    pipeline = [(cf.CoordinateFrame(naxes=1, axes_type=("PIXEL",), axes_order=(0,), name='detector'), trans3),
+                (cf.CoordinateFrame(naxes=1, axes_type=("SPATIAL",), axes_order=(0,), name='sky'), None)]
     w = wcs.WCS(pipeline)
     w.bounding_box = ((-1, 10), (6, 15), (4.3, 6.9))
 
@@ -608,11 +609,13 @@ def setup_class(self):
         tan = models.Pix2Sky_TAN(name='tangent_projection')
         sky_cs = cf.CelestialFrame(reference_frame=coord.ICRS(), name='sky')
         det = cf.Frame2D(name='detector')
+        focal = cf.Frame2D(name='focal')
         wcs_forward = wcslin | tan | n2c
-        pipeline = [wcs.Step('detector', distortion),
-                    wcs.Step('focal', wcs_forward),
-                    wcs.Step(sky_cs, None)
-                    ]
+        pipeline = [
+            wcs.Step(det, distortion),
+            wcs.Step(focal, wcs_forward),
+            wcs.Step(sky_cs, None)
+        ]
 
         self.wcs = wcs.WCS(input_frame=det,
                            output_frame=sky_cs,
@@ -659,7 +662,7 @@ def test_inverse(self):
 
     def test_back_coordinates(self):
         sky_coord = self.wcs(1, 2, with_units=True)
-        res = self.wcs.transform('sky', 'focal', sky_coord, with_units=True)
+        res = self.wcs.transform('sky', 'focal', sky_coord, with_units=False)
         assert_allclose(res, self.wcs.get_transform('detector', 'focal')(1, 2))
 
     def test_units(self):
@@ -1553,9 +1556,8 @@ def test_high_level_objects_in_pipeline_forward(gwcs_with_pipeline_celestial):
         *input_pixel,
         with_units=True
     )
-    assert len(intermediate_world_with_units) == 1
-    assert isinstance(intermediate_world_with_units[0], coord.SkyCoord)
-    sc = intermediate_world_with_units[0]
+    assert isinstance(intermediate_world_with_units, coord.SkyCoord)
+    sc = intermediate_world_with_units
     assert u.allclose(sc.ra, 20*u.arcsec)
     assert u.allclose(sc.dec, 15*u.deg)
 
diff --git a/gwcs/wcs.py b/gwcs/wcs.py
index 8c99b753..62fcb01d 100644
--- a/gwcs/wcs.py
+++ b/gwcs/wcs.py
@@ -1153,8 +1153,8 @@ def transform(self, from_frame, to_frame, *args, **kwargs):
         to_frame = self._get_frame_by_name(to_frame)
 
         with_units = kwargs.pop("with_units", False)
-        if with_units and backward:
-            args = high_level_objects_to_values(*args, low_level_wcs=self)
+        if backward and utils.is_high_level(*args, low_level_wcs=from_frame):
+            args = high_level_objects_to_values(*args, low_level_wcs=from_frame)
 
         results = self._call_forward(*args, from_frame=from_frame, to_frame=to_frame, **kwargs)