diff --git a/graphene/pyutils/enum.py b/graphene/pyutils/enum.py
index 8c09a6ad..928d0be2 100644
--- a/graphene/pyutils/enum.py
+++ b/graphene/pyutils/enum.py
@@ -71,18 +71,18 @@ def _is_descriptor(obj):
 
 def _is_dunder(name):
     """Returns True if a __dunder__ name, False otherwise."""
-    return (name[:2] == name[-2:] == '__' and
+    return (len(name) > 4 and
+            name[:2] == name[-2:] == '__' and
             name[2:3] != '_' and
-            name[-3:-2] != '_' and
-            len(name) > 4)
+            name[-3:-2] != '_')
 
 
 def _is_sunder(name):
     """Returns True if a _sunder_ name, False otherwise."""
-    return (name[0] == name[-1] == '_' and
+    return (len(name) > 2 and
+            name[0] == name[-1] == '_' and
             name[1:2] != '_' and
-            name[-2:-1] != '_' and
-            len(name) > 2)
+            name[-2:-1] != '_')
 
 
 def _make_class_unpicklable(cls):
diff --git a/graphene/pyutils/tests/__init__.py b/graphene/pyutils/tests/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/graphene/pyutils/tests/test_enum.py b/graphene/pyutils/tests/test_enum.py
new file mode 100644
index 00000000..bf15a620
--- /dev/null
+++ b/graphene/pyutils/tests/test_enum.py
@@ -0,0 +1,41 @@
+from ..enum import _is_dunder, _is_sunder
+
+
+def test__is_dunder():
+    dunder_names = [
+        '__i__',
+        '__test__',
+    ]
+    non_dunder_names = [
+        'test',
+        '__test',
+        '_test',
+        '_test_',
+        'test__',
+        '',
+    ]
+
+    for name in dunder_names:
+        assert _is_dunder(name) is True
+
+    for name in non_dunder_names:
+        assert _is_dunder(name) is False
+
+def test__is_sunder():
+    sunder_names = [
+        '_i_',
+        '_test_',
+    ]
+
+    non_sunder_names = [
+        '__i__',
+        '_i__',
+        '__i_',
+        '',
+    ]
+
+    for name in sunder_names:
+        assert _is_sunder(name) is True
+
+    for name in non_sunder_names:
+        assert _is_sunder(name) is False