diff --git a/Lib/glyphsLib/builder/instances.py b/Lib/glyphsLib/builder/instances.py
index 7d518da93..89615b2be 100644
--- a/Lib/glyphsLib/builder/instances.py
+++ b/Lib/glyphsLib/builder/instances.py
@@ -389,8 +389,10 @@ def apply_instance_data_to_ufo(ufo, instance, designspace):
     Returns:
         None.
     """
-    set_weight_class(ufo, designspace, instance)
-    set_width_class(ufo, designspace, instance)
+    if any(axis.tag == "wght" for axis in designspace.axes):
+        set_weight_class(ufo, designspace, instance)
+    if any(axis.tag == "wdth" for axis in designspace.axes):
+        set_width_class(ufo, designspace, instance)
 
     glyphs_instance = InstanceDescriptorAsGSInstance(instance)
     to_ufo_custom_params(None, ufo, glyphs_instance)
diff --git a/tests/builder/instances_test.py b/tests/builder/instances_test.py
index ec31ef58c..21bea228f 100644
--- a/tests/builder/instances_test.py
+++ b/tests/builder/instances_test.py
@@ -67,8 +67,17 @@ def test_apply_instance_data(tmpdir, instance_names):
     assert len(ufos) == len(test_instances)
 
     for ufo in ufos:
-        assert ufo.info.openTypeOS2WeightClass is not None
-        assert ufo.info.openTypeOS2WidthClass is not None
+        assert ufo.info.openTypeOS2WeightClass in {
+            100,
+            200,
+            300,
+            400,
+            500,
+            700,
+            900,
+            357,
+        }
+        assert ufo.info.openTypeOS2WidthClass is None  # GlyphsUnitTestSans is wght only
 
 
 def test_reexport_apply_instance_data():