diff --git a/newsfragments/699.bugfix b/newsfragments/699.bugfix
new file mode 100644
index 000000000..66e598963
--- /dev/null
+++ b/newsfragments/699.bugfix
@@ -0,0 +1 @@
+Fix bug when setting the distance for single panel detectors that have a hierarchy.
diff --git a/src/dxtbx/model/detector_helpers.py b/src/dxtbx/model/detector_helpers.py
index 3240caf7e..5810638d7 100644
--- a/src/dxtbx/model/detector_helpers.py
+++ b/src/dxtbx/model/detector_helpers.py
@@ -303,34 +303,31 @@ def set_detector_distance(detector, distance):
     """
     Set detector origin from distance along normal
     """
-    # If the detector has a hierarchy, just update the root note
-    try:
-        h = detector.hierarchy()
-        normal = matrix.col(h.get_normal())
-        origin = matrix.col(h.get_origin())
+    panels = list(detector)
+    if len(panels) > 1:
+        # If a multi-panel detector has a hierarchy, we will just update the
+        # root note. Otherwise check that all panels are at the same distance
+        # and share the same normal vector
+        try:
+            panels = [
+                detector.hierarchy(),
+            ]
+        except AttributeError:
+            dists = [p.get_distance() for p in panels]
+            norm_vecs = [p.get_normal() for p in panels]
+            assert all(v == norm_vecs[0] for v in norm_vecs[1:]) and all(
+                d == dists[0] for d in dists
+            )
+
+    for panel in panels:
+        normal = matrix.col(panel.get_normal())
+        origin = matrix.col(panel.get_origin())
         d = origin.dot(normal)
         x = origin - d * normal
         origin = distance * normal + x
-        fast_axis = h.get_fast_axis()
-        slow_axis = h.get_slow_axis()
-        h.set_frame(fast_axis, slow_axis, origin)
-    except AttributeError:
-        # Check all panels are at the same distance and share the same normal
-        dists = [p.get_distance() for p in detector]
-        norm_vecs = [p.get_normal() for p in detector]
-        assert all(v == norm_vecs[0] for v in norm_vecs[1:]) and all(
-            d == dists[0] for d in dists
-        )
-
-        for panel in detector:
-            normal = matrix.col(panel.get_normal())
-            origin = matrix.col(panel.get_origin())
-            d = origin.dot(normal)
-            x = origin - d * normal
-            origin = distance * normal + x
-            fast_axis = panel.get_fast_axis()
-            slow_axis = panel.get_slow_axis()
-            panel.set_frame(fast_axis, slow_axis, origin)
+        fast_axis = panel.get_fast_axis()
+        slow_axis = panel.get_slow_axis()
+        panel.set_frame(fast_axis, slow_axis, origin)
 
 
 def get_detector_projection_2d_axes(