diff --git a/src/virtual-counters-manager.js b/src/virtual-counters-manager.js
index c2de1442..143c86e1 100644
--- a/src/virtual-counters-manager.js
+++ b/src/virtual-counters-manager.js
@@ -136,7 +136,7 @@ module.exports = class VirtualCountersManager {
             spentCountersByFunction[this.calledFunc] = spentCounters;
         } else {
             Object.keys(this.currentCountersSnapshot).forEach((counter) => {
-                spentCountersByFunction[this.calledFunc][counter] = spentCountersByFunction[this.calledFunc][counter] + spentCounters[counter];
+                spentCountersByFunction[this.calledFunc][counter] += spentCounters[counter];
             });
         }