diff --git a/index.js b/index.js
index 7684d23..efa8fee 100644
--- a/index.js
+++ b/index.js
@@ -40,7 +40,7 @@ function hasBinary(data) {
           }
       }
     } else if (obj && 'object' == typeof obj) {
-      if (obj.toJSON) {
+      if (obj.toJSON && 'function' == typeof obj.toJSON) {
         obj = obj.toJSON();
       }
 
diff --git a/test.js b/test.js
index 5320d4f..8d9247c 100644
--- a/test.js
+++ b/test.js
@@ -22,12 +22,12 @@ describe('has-binarydata', function(){
   });
 
   it('should work with an object that does not contain binary', function() {
-    var ob = {a: 'a', b: [], c: 1234};
+    var ob = {a: 'a', b: [], c: 1234, toJSON: '{\"a\": \"a\"}'};
     assert(!hasBinary(ob));
   });
 
   it('should work with an object that contains a buffer', function() {
-    var ob = {a: 'a', b: new Buffer('abc'), c: 1234};
+    var ob = {a: 'a', b: new Buffer('abc'), c: 1234, toJSON: '{\"a\": \"a\"}'};
     assert(hasBinary(ob));
   });