diff --git a/files/system-monitor-graph@rcassani/desklet.js b/files/system-monitor-graph@rcassani/desklet.js
index 623df33..72beb9f 100644
--- a/files/system-monitor-graph@rcassani/desklet.js
+++ b/files/system-monitor-graph@rcassani/desklet.js
@@ -216,7 +216,7 @@ SystemMonitorGraph.prototype = {
         }
 
         // concatenate new value
-        values.push(value);
+        values.push(isNaN(value) ? 0 : value);
         values.shift();
         this.values = values;