diff --git a/NSspi/Contexts/Context.cs b/NSspi/Contexts/Context.cs
index e763e26..a955a1f 100644
--- a/NSspi/Contexts/Context.cs
+++ b/NSspi/Contexts/Context.cs
@@ -110,6 +110,10 @@ namespace NSspi.Contexts
             {
                 throw new InvalidOperationException( "The context is not fully formed." );
             }
+            else if( this.Disposed )
+            {
+                throw new ObjectDisposedException( "Context" );
+            }
 
             sizes = QueryBufferSizes();
 
@@ -186,6 +190,10 @@ namespace NSspi.Contexts
             {
                 throw new InvalidOperationException( "The context is not fully formed." );
             }
+            else if( this.Disposed )
+            {
+                throw new ObjectDisposedException( "Context" );
+            }
 
             sizes = QueryBufferSizes();