diff --git a/jnius/jnius_export_class.pxi b/jnius/jnius_export_class.pxi
index 6fcfe07..9d4dd1f 100644
--- a/jnius/jnius_export_class.pxi
+++ b/jnius/jnius_export_class.pxi
@@ -128,7 +128,15 @@ class MetaJavaClass(MetaJavaBase):
             if jcs is not None:
                 obj = jcs.j_cls
 
-        if NULL != obj:
+        if NULL == obj:
+            if isinstance(value, PythonJavaClass):
+                for interface in getattr(value, '__javainterfaces__', []):
+                    obj = j_env[0].FindClass(j_env, interface)
+                    if obj == NULL:
+                        j_env[0].ExceptionClear(j_env)
+                    elif 0 != j_env[0].IsAssignableFrom(j_env, obj, me.j_cls):
+                        return True
+        else:
             if 0 != j_env[0].IsAssignableFrom(j_env, obj, me.j_cls):
                 return True