diff --git a/build/index.js b/build/index.js
index 9321804..27ba570 100644
--- a/build/index.js
+++ b/build/index.js
@@ -76,7 +76,9 @@ function jsonp(url, options) {
             cleanup();
             resolve(data);
         };
-        params[callback] = id;
+        if (!callbackName) {
+            params[callback] = id;
+        }
         url = handleUrl(url, params);
         // Create script.
         script = document.createElement('script');
diff --git a/package.json b/package.json
index 068c1ff..48b83cc 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "simple-jsonp-promise",
-  "version": "1.0.9",
+  "version": "1.1.0",
   "description": "",
   "main": "build/index.js",
   "scripts": {
diff --git a/src/index.js b/src/index.js
index af0c461..afb3b5f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -26,7 +26,7 @@ function jsonp(url, options) {
     let timer;
     let promise;
     // Generate a unique id for the request.
-    let id = callbackName || (prefix + (count++));
+    let id = callbackName || prefix + count++;
 
     function noop() {}
 
@@ -69,7 +69,9 @@ function jsonp(url, options) {
             cleanup();
             resolve(data);
         };
-        params[callback] = id;
+        if (!callbackName) {
+            params[callback] = id;
+        }
         url = handleUrl(url, params);
         // Create script.
         script = document.createElement('script');