diff --git a/HMACAuthentication.WebApi/Filters/HMACAuthenticationAttribute.cs b/HMACAuthentication.WebApi/Filters/HMACAuthenticationAttribute.cs
index 18c6da3..b581c0d 100644
--- a/HMACAuthentication.WebApi/Filters/HMACAuthenticationAttribute.cs
+++ b/HMACAuthentication.WebApi/Filters/HMACAuthenticationAttribute.cs
@@ -151,8 +151,9 @@ private bool isReplayRequest(string nonce, string requestTimeStamp)
 
             var serverTotalSeconds = Convert.ToUInt64(currentTs.TotalSeconds);
             var requestTotalSeconds = Convert.ToUInt64(requestTimeStamp);
+            ulong difference = serverTotalSeconds > requestTotalSeconds ? serverTotalSeconds - requestTotalSeconds : requestTotalSeconds - serverTotalSeconds;
 
-            if ((serverTotalSeconds - requestTotalSeconds) > requestMaxAgeInSeconds)
+            if (difference > requestMaxAgeInSeconds)
             {
                 return true;
             }