diff --git a/Sources/AppAuthCore/OIDFieldMapping.m b/Sources/AppAuthCore/OIDFieldMapping.m
index f84365602..680fb966e 100644
--- a/Sources/AppAuthCore/OIDFieldMapping.m
+++ b/Sources/AppAuthCore/OIDFieldMapping.m
@@ -96,7 +96,8 @@ + (NSSet *)JSONTypes {
     [NSDictionary class],
     [NSArray class],
     [NSString class],
-    [NSNumber class]
+    [NSNumber class],
+    [NSNull class],
   ]];
 }