diff --git a/Source/Collections/ObservableSet.cs b/Source/Collections/ObservableSet.cs
index 84d6c77..f142888 100644
--- a/Source/Collections/ObservableSet.cs
+++ b/Source/Collections/ObservableSet.cs
@@ -27,6 +27,8 @@ using System.Collections;
 using System.Collections.Specialized;
 #endif
 
+#if !(WINDOWS_PHONE || XBOX360)
+
 namespace Nuclex.Support.Collections {
 
   /// <summary>Set which fires events when items are removed or added to it</summary>
@@ -309,3 +311,5 @@ namespace Nuclex.Support.Collections {
   }
 
 } // namespace Nuclex.Support.Collections
+
+#endif // !(WINDOWS_PHONE || XBOX360)
diff --git a/Source/Collections/ReadOnlySet.cs b/Source/Collections/ReadOnlySet.cs
index 9ef771c..f4dd1ca 100644
--- a/Source/Collections/ReadOnlySet.cs
+++ b/Source/Collections/ReadOnlySet.cs
@@ -22,6 +22,8 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 
+#if !(WINDOWS_PHONE || XBOX360)
+
 namespace Nuclex.Support.Collections {
 
   /// <summary>Wraps a set and prevents it from being modified</summary>
@@ -210,3 +212,5 @@ namespace Nuclex.Support.Collections {
   }
 
 } // namespace Nuclex.Support.Collections
+
+#endif // !(WINDOWS_PHONE || XBOX360)