diff --git a/clusterize.js b/clusterize.js
index 0682267..1de7429 100644
--- a/clusterize.js
+++ b/clusterize.js
@@ -195,7 +195,7 @@
     },
     // get current cluster number
     getClusterNum: function () {
-      this.options.scroll_top = this.scroll_elem.scrollTop;
+      this.options.scroll_top = this.scroll_elem.scrollTop - this.content_elem.offsetTop;
       return Math.floor(this.options.scroll_top / (this.options.cluster_height - this.options.block_height)) || 0;
     },
     // generate empty row if no data provided
@@ -328,4 +328,4 @@
   }
 
   return Clusterize;
-}));
\ No newline at end of file
+}));