diff --git a/src/capture-metrics.js b/src/capture-metrics.js
index 464bd7b37..0aafe2801 100644
--- a/src/capture-metrics.js
+++ b/src/capture-metrics.js
@@ -5,9 +5,16 @@ export class CaptureMetrics {
     }
 
     incr(key, by = 1) {
-        key = `phjs-${key}`
         if (this.capture) {
+            key = `phjs-${key}`
             this.metrics[key] = (this.metrics[key] || 0) + by
         }
     }
+
+    decr(key) {
+        if (this.capture) {
+            key = `phjs-${key}`
+            this.metrics[key] = (this.metrics[key] || 0) - 1
+        }
+    }
 }
diff --git a/src/posthog-core.js b/src/posthog-core.js
index d6c3150b5..e576ccff6 100644
--- a/src/posthog-core.js
+++ b/src/posthog-core.js
@@ -372,6 +372,7 @@ PostHogLib.prototype._send_request = function (url, data, options, callback) {
     this._captureMetrics.incr('_send_request')
     this._captureMetrics.incr(`_send_request_${options.transport}`)
     this._captureMetrics.incr(`_send_request_${classifier}`)
+    this._captureMetrics.incr('_send_request_inflight')
 
     // needed to correctly format responses
     var verbose_mode = this.get_config('verbose')
@@ -451,6 +452,7 @@ PostHogLib.prototype._send_request = function (url, data, options, callback) {
                     this._captureMetrics.incr(`xhr-response`)
                     this._captureMetrics.incr(`xhr-response-${req.status}`)
                     this._captureMetrics.incr(`xhr-done-${classifier}-${req.status}`)
+                    this._captureMetrics.decr('_send_request_inflight')
                     // XMLHttpRequest.DONE == 4, except in safari 4
                     if (req.status === 200) {
                         if (callback) {