diff --git a/Src/zipkin4net.middleware.aspnetcore/Src/TracingMiddleware.cs b/Src/zipkin4net.middleware.aspnetcore/Src/TracingMiddleware.cs
index e26e8f0..aa869e8 100644
--- a/Src/zipkin4net.middleware.aspnetcore/Src/TracingMiddleware.cs
+++ b/Src/zipkin4net.middleware.aspnetcore/Src/TracingMiddleware.cs
@@ -22,7 +22,10 @@ public static void UseTracing(this IApplicationBuilder app, string serviceName,
                 Trace.Current = trace;
                 using (var serverTrace = new ServerTrace(serviceName, getRpc(context)))
                 {
-                    trace.Record(Annotations.Tag("http.host", request.Host.ToString()));
+                    if (request.Host.HasValue)
+                    {
+                        trace.Record(Annotations.Tag("http.host", request.Host.ToString()));
+                    }
                     trace.Record(Annotations.Tag("http.uri", UriHelper.GetDisplayUrl(request)));
                     trace.Record(Annotations.Tag("http.path", request.Path));
                     await serverTrace.TracedActionAsync(next());