diff --git a/lib/publickey.js b/lib/publickey.js
index 94c22e0..e8fc58f 100644
--- a/lib/publickey.js
+++ b/lib/publickey.js
@@ -131,7 +131,7 @@ PublicKey._isBuffer = function(param) {
  * @private
  */
 PublicKey._isJSON = function(json) {
-  return JSUtil.isValidJSON(json) || (json.x && json.y);
+  return !!(JSUtil.isValidJSON(json) || (json.x && json.y));
 };
 
 /**
diff --git a/test/publickey.js b/test/publickey.js
index 62ca8ff..7220751 100644
--- a/test/publickey.js
+++ b/test/publickey.js
@@ -147,6 +147,8 @@ describe('PublicKey', function() {
       expect(function() {
         return PublicKey.fromJSON('{"x": "1ff0fe0f7b15ffaa85ff9f4744d539139c252a49710fb053bb9f2b933173ff9a"}');
       }).to.throw();
+      // coverage
+      PublicKey._isJSON({x: '1ff0fe0f7b15ffaa85ff9f4744d539139c252a49710fb053bb9f2b933173ff9a'}).should.equal(false);
     });
 
     it('fails if invalid JSON is provided', function() {