diff --git a/graphene/types/typemap.py b/graphene/types/typemap.py
index ecaedf75..c2b47279 100644
--- a/graphene/types/typemap.py
+++ b/graphene/types/typemap.py
@@ -10,6 +10,7 @@ from graphql.execution.executor import get_default_resolve_type_fn
 from graphql.type.typemap import GraphQLTypeMap
 
 from ..utils.str_converters import to_camel_case
+from ..utils.get_unbound_function import get_unbound_function
 from .dynamic import Dynamic
 from .enum import Enum
 from .inputobjecttype import InputObjectType
@@ -251,11 +252,10 @@ class TypeMap(GraphQLTypeMap):
                 if interface_resolver:
                     break
             resolver = interface_resolver
+
         # Only if is not decorated with classmethod
         if resolver:
-            if not getattr(resolver, '__self__', True):
-                return resolver.__func__
-            return resolver
+            return get_unbound_function(resolver)
 
         return partial(self.default_resolver, name, default_value)
 
diff --git a/graphene/utils/get_unbound_function.py b/graphene/utils/get_unbound_function.py
new file mode 100644
index 00000000..64add00a
--- /dev/null
+++ b/graphene/utils/get_unbound_function.py
@@ -0,0 +1,4 @@
+def get_unbound_function(func):
+    if not getattr(func, '__self__', True):
+        return func.__func__
+    return func