diff --git a/src/Libraries/Microsoft.Extensions.Http.Diagnostics/Latency/Internal/HttpRequestLatencyListener.cs b/src/Libraries/Microsoft.Extensions.Http.Diagnostics/Latency/Internal/HttpRequestLatencyListener.cs
index 5d7238ed8a3..4179759df35 100644
--- a/src/Libraries/Microsoft.Extensions.Http.Diagnostics/Latency/Internal/HttpRequestLatencyListener.cs
+++ b/src/Libraries/Microsoft.Extensions.Http.Diagnostics/Latency/Internal/HttpRequestLatencyListener.cs
@@ -49,7 +49,9 @@ public void Enable()
     internal void OnEventWritten(string eventSourceName, string? eventName)
     {
         // If event of interest, add a checkpoint for it.
-        if (eventName != null && _eventToTokenMap[eventSourceName].TryGetValue(eventName, out var token))
+        if (eventName != null
+            && _eventToTokenMap.TryGetValue(eventSourceName, out var tokenMap)
+            && tokenMap.TryGetValue(eventName, out var token))
         {
             LatencyContext.Get()?.AddCheckpoint(token);
         }
diff --git a/test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpRequestLatencyListenerTest.cs b/test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpRequestLatencyListenerTest.cs
index fa91daa1c3e..6b384eae928 100644
--- a/test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpRequestLatencyListenerTest.cs
+++ b/test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpRequestLatencyListenerTest.cs
@@ -191,4 +191,19 @@ public void HttpRequestLatencyListener_OnEventWritten_AddsCheckpoints_Http()
         lc.Verify(a => a.AddCheckpoint(It.IsAny<CheckpointToken>()),
             Times.Exactly(numHttpEvents + numSocketEvents + numDnsEvents));
     }
+
+    [Fact]
+    public void HttpRequestLatencyListener_OnEventWritten_DoesNotAddCheckpoints_UnknownEventSource()
+    {
+        var lcti = HttpMockProvider.GetTokenIssuer();
+        var lc = HttpMockProvider.GetLatencyContext();
+        var context = new HttpClientLatencyContext();
+        context.Set(lc.Object);
+
+        using var listener = HttpMockProvider.GetListener(context, lcti.Object);
+
+        listener.OnEventWritten("System.Runtime", "EventCounters");
+
+        lc.Verify(a => a.AddCheckpoint(It.IsAny<CheckpointToken>()), Times.Never);
+    }
 }