diff --git a/index.js b/index.js
index a8f0851..434ccfa 100644
--- a/index.js
+++ b/index.js
@@ -40,7 +40,8 @@ function hasBinary(data) {
           }
       }
     } else if (obj && 'object' == typeof obj) {
-      if (obj.toJSON) {
+      // see: https://github.com/Automattic/has-binary/pull/4
+      if (obj.toJSON && 'function' == typeof obj.toJSON) {
         obj = obj.toJSON();
       }