diff --git a/Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveService.cs b/Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveService.cs
index c3f4740..0f9f127 100644
--- a/Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveService.cs
+++ b/Lib.AspNetCore.ServerSentEvents/ServerSentEventsKeepaliveService.cs
@@ -76,9 +76,9 @@ private async Task ExecuteAsync(CancellationToken stoppingToken)
 
         private static bool IsBehindAncm()
         {
-            return !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_PORT"))
-                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_APPL_PATH"))
-                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable($"ASPNETCORE_TOKEN"));
+            return !String.IsNullOrEmpty(Environment.GetEnvironmentVariable("ASPNETCORE_PORT"))
+                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable("ASPNETCORE_APPL_PATH"))
+                && !String.IsNullOrEmpty(Environment.GetEnvironmentVariable("ASPNETCORE_TOKEN"));
         }
 
         public virtual void Dispose()