diff --git a/Lidgren.Network/NetReservedAddress.cs b/Lidgren.Network/NetReservedAddress.cs
index ea69315..fba91c5 100644
--- a/Lidgren.Network/NetReservedAddress.cs
+++ b/Lidgren.Network/NetReservedAddress.cs
@@ -45,7 +45,7 @@ public static bool IsAddressReserved(IPAddress address)
 
 			foreach (var (reservedIp, maskBits) in ReservedRanges)
 			{
-				var mask = uint.MaxValue << maskBits;
+				var mask = uint.MaxValue << (32 - maskBits);
 				if ((ipBits & mask) == (reservedIp & mask))
 					return true;
 			}