1 files changed, 1 insertions, 2 deletions
diff --git a/src/DotNetOpenAuth.OAuth/OAuth/ServiceProviderDescription.cs b/src/DotNetOpenAuth.OAuth/OAuth/ServiceProviderDescription.cs
index 3f553a9..6dbe6ea 100644
--- a/src/DotNetOpenAuth.OAuth/OAuth/ServiceProviderDescription.cs
+++ b/src/DotNetOpenAuth.OAuth/OAuth/ServiceProviderDescription.cs
@@ -8,7 +8,6 @@ namespace DotNetOpenAuth.OAuth {
 	using System;
 	using System.Diagnostics;
 	using System.Diagnostics.CodeAnalysis;
-	using System.Diagnostics.Contracts;
 	using System.Linq;
 	using DotNetOpenAuth.Messaging;
 	using DotNetOpenAuth.OAuth.ChannelElements;
@@ -95,7 +94,7 @@ namespace DotNetOpenAuth.OAuth {
 		/// </summary>
 		/// <returns>The created signing element.</returns>
 		internal ITamperProtectionChannelBindingElement CreateTamperProtectionElement() {
-			Contract.Requires(this.TamperProtectionElements != null);
+			RequiresEx.ValidState(this.TamperProtectionElements != null);
 			return new SigningBindingElementChain(this.TamperProtectionElements.Select(el => (ITamperProtectionChannelBindingElement)el.Clone()).ToArray());
 		}
 	}