diff --git a/lib/process_metrics.js b/lib/process_metrics.js
index 44ad55eb..bcccfae8 100644
--- a/lib/process_metrics.js
+++ b/lib/process_metrics.js
@@ -50,7 +50,7 @@ var process_metrics = function (metrics, flushInterval, ts, flushCallback) {
           }
 
           var clean_pct = '' + pct;
-          clean_pct.replace('.', '_');
+          clean_pct = clean_pct.replace('.', '_');
           current_timer_data["mean_" + clean_pct] = mean;
           current_timer_data["upper_" + clean_pct] = maxAtThreshold;
           current_timer_data["sum_" + clean_pct] = sum;