diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3c3629e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+node_modules
diff --git a/lib/gateway.js b/lib/gateway.js
index 435331b..9b2b851 100644
--- a/lib/gateway.js
+++ b/lib/gateway.js
@@ -184,9 +184,10 @@ Gateway.prototype.reportMetrics = function reportMetrics( ) {
     samples = samples.splice(0);
 
     // discard samples older than the configured cutoff
-    if (this.maxMetricAgeMs >= 0) {
-        var now = this.getTimestamp();
-        var oldestKeepTs = now - this.maxMetricAgeMs;
+    const now = this.getTimestamp();
+    const oldestKeepTs = this.maxMetricAgeMs >= 0 ? (now - this.maxMetricAgeMs) : 0;
+    const filterOldMetrics = this.maxMetricAgeMs >= 0;
+    if (filterOldMetrics) {
         for (i=0; i<samples.length && samples[i].ts < oldestKeepTs; i++) ;
         if (i > 0) {
             Gateway.trace("discarding %d samples older than %d ms, from %d to %d",
@@ -210,10 +211,19 @@ Gateway.prototype.reportMetrics = function reportMetrics( ) {
 
     for (i=0; i<averages.length; i++) averages[i].value /= averages[i].count;
 
-    // never omit any known metrics, report the previous value if no change
+    // Don't omit any known metrics, report the previous value if no change
+    // except for metrics older than the configured cutoff.
     // This allows /metrics to be called more frequently than the /push interval.
     var allValues = {};
-    for (id in this.previousValues) allValues[id] = this.previousValues[id];
+    for (id in this.previousValues) {
+        if (!filterOldMetrics || this.previousValues[id].ts >= oldestKeepTs) {
+            allValues[id] = this.previousValues[id];
+        }
+    }
+    const discardedMetrics = Object.keys(this.previousValues).length - Object.keys(allValues).length;
+    if (discardedMetrics > 0) {
+        Gateway.trace("discarding %d metrics older than %d ms", discardedMetrics, this.maxMetricAgeMs);
+    }
     for (id in map) allValues[id] = map[id];
     this.previousValues = allValues;