diff --git a/terracotta/server/fields.py b/terracotta/server/fields.py
index af758299..0a4b9d84 100644
--- a/terracotta/server/fields.py
+++ b/terracotta/server/fields.py
@@ -30,5 +30,3 @@ def validate_stretch_range(data: Any) -> None:
     if isinstance(data, str):
         if not re.match("^p\\d+$", data):
             raise ValidationError("Percentile format is `p<digits>`")
-    elif not isinstance(data, (int, float)):
-        raise ValidationError("Must be a number or string like `p<digits>`")
diff --git a/tests/server/test_fields.py b/tests/server/test_fields.py
new file mode 100644
index 00000000..34d13fd7
--- /dev/null
+++ b/tests/server/test_fields.py
@@ -0,0 +1,42 @@
+from marshmallow import ValidationError
+import pytest
+from terracotta.server.singleband import SinglebandOptionSchema
+
+
+@pytest.mark.parametrize(
+    "args, expected",
+    [("[0, 1]", [0, 1]), ('["p2", "p28"]', ["p2", "p28"]), (None, None)],
+)
+def test_serde(args, expected):
+    args = {"stretch_range": args}
+    option_schema = SinglebandOptionSchema()
+    loaded = option_schema.load(args)
+    assert loaded["stretch_range"] == expected
+    dumped = option_schema.dump(loaded)
+    assert dumped["stretch_range"] == expected
+
+
+def test_serde_validation():
+    option_schema = SinglebandOptionSchema()
+    with pytest.raises(ValidationError) as exc_info:
+        args = {"stretch_range": '["t2", "p28"]'}
+        option_schema.load(args)
+    assert "Percentile format is `p<digits>`" in str(exc_info.value)
+
+    with pytest.raises(ValidationError) as exc_info:
+        args = {"stretch_range": '[{}, "p28"]'}
+        option_schema.load(args)
+    assert "Must be a string or a number" in str(exc_info.value)
+
+
+def test_serde_bad_type():
+    option_schema = SinglebandOptionSchema()
+    with pytest.raises(ValidationError) as exc_info:
+        dump_args = {"stretch_range": [0, {"bad": "type"}]}
+        option_schema.dump(dump_args)
+    assert "Must be a string or a number" in str(exc_info.value)
+
+    with pytest.raises(ValidationError) as exc_info:
+        load_args = {"stretch_range": '[0, {"bad": "type"}]'}
+        option_schema.load(load_args)
+    assert "Must be a string or a number" in str(exc_info.value)