diff --git a/glue/config_gen.py b/glue/config_gen.py
old mode 100755
new mode 100644
diff --git a/glue/core/state_objects.py b/glue/core/state_objects.py
index 26f98b28d..6262964ed 100644
--- a/glue/core/state_objects.py
+++ b/glue/core/state_objects.py
@@ -332,7 +332,9 @@ def update_values(self, force=False, use_default_modifiers=False, **properties):
 
         self._previous_units = display_units
 
-        if set(properties) == {'display_units'}:
+        if (set(properties) == {'display_units'} and
+                self.lower is not None and
+                self.upper is not None):
 
             converter = UnitConverter()
 
diff --git a/glue/main.py b/glue/main.py
old mode 100755
new mode 100644
diff --git a/glue/viewers/image/state.py b/glue/viewers/image/state.py
index e9eac8aaa..a40346893 100644
--- a/glue/viewers/image/state.py
+++ b/glue/viewers/image/state.py
@@ -536,8 +536,7 @@ def format_unit(unit):
 
         ImageLayerState.attribute_display_unit.set_display_func(self, format_unit)
 
-        self.add_callback('attribute', self._update_attribute_display_unit_choices)
-        # self.add_callback('attribute_display_unit', self._convert_attribute_limits_units, echo_old=True)
+        self.add_callback('attribute', self._update_attribute_display_unit_choices, priority=10000)
 
         self._update_attribute_display_unit_choices()
 
diff --git a/glue/viewers/matplotlib/tests/test_state.py b/glue/viewers/matplotlib/tests/test_state.py
old mode 100755
new mode 100644