diff --git a/t5/data/glue_utils.py b/t5/data/glue_utils.py
index 66378ea0..bb933bde 100644
--- a/t5/data/glue_utils.py
+++ b/t5/data/glue_utils.py
@@ -113,6 +113,7 @@ def get_glue_postprocess_fn(builder_config):
     return functools.partial(
         postprocessors.string_label_to_class_id,
         label_classes=builder_config.label_classes,
+        use_default=False,
     )
 
 GLUE_METRICS = collections.OrderedDict([
diff --git a/t5/data/postprocessors.py b/t5/data/postprocessors.py
index 5c4aaa31..7f413e4b 100644
--- a/t5/data/postprocessors.py
+++ b/t5/data/postprocessors.py
@@ -41,12 +41,16 @@ def lower_text(string, **unused_kwargs):
 def string_label_to_class_id(string_label,
                              label_classes,
                              default=-1,
+                             use_default=True,
                              **unused_kwargs):
   """Returns index of string_label in label_classes or default if not found."""
   if string_label in label_classes:
     return label_classes.index(string_label)
   else:
-    return default
+    if use_default:
+      return default
+    else:
+      return string_label
 
 
 def multirc(string_label, example=None, is_target=False):
diff --git a/t5/data/postprocessors_test.py b/t5/data/postprocessors_test.py
index c315d6bb..9b254718 100644
--- a/t5/data/postprocessors_test.py
+++ b/t5/data/postprocessors_test.py
@@ -36,6 +36,8 @@ def test_string_label_to_class_id(self):
     self.assertEqual(postprocessors.string_label_to_class_id("two", cls), 1)
     self.assertEqual(postprocessors.string_label_to_class_id("foo", cls), -1)
     self.assertEqual(postprocessors.string_label_to_class_id("foo", cls, 2), 2)
+    self.assertEqual(postprocessors.string_label_to_class_id(
+        "foo", cls, use_default=False), "foo")
 
   def test_multirc(self):
     self.assertDictEqual(