diff --git a/mcs/class/corlib/System.IO/Stream.cs b/mcs/class/corlib/System.IO/Stream.cs
index 17c8cc457eb82bc3b2733a00659fb5546c423e09..eeaedd8b15ad1e32f00f20fa69cd2954a8aad11f 100644
--- a/mcs/class/corlib/System.IO/Stream.cs
+++ b/mcs/class/corlib/System.IO/Stream.cs
@@ -105,6 +105,7 @@ namespace System.IO
 		public virtual void Close ()
 		{
 			Dispose (true);
+			GC.SuppressFinalize (this);
 		}
 
 		[ComVisible (false)]
diff --git a/mcs/class/corlib/System.Security.Cryptography/CryptoStream.cs b/mcs/class/corlib/System.Security.Cryptography/CryptoStream.cs
index 7eb680847ec7e701ba50be60bbabcb14d2c0cf6f..63f310885dc07a607ba01db2757d4e119a0cfab0 100644
--- a/mcs/class/corlib/System.Security.Cryptography/CryptoStream.cs
+++ b/mcs/class/corlib/System.Security.Cryptography/CryptoStream.cs
@@ -109,19 +109,13 @@ namespace System.Security.Cryptography {
 
 		public void Clear () 
 		{
-			Dispose (true);
-			GC.SuppressFinalize (this); // not called in Stream.Dispose
+			Close ();
 		}
 
 		// LAMESPEC: A CryptoStream can be close in read mode
 		public override void Close () 
 		{
-			// only flush in write mode (bugzilla 46143)
-			if ((!_flushedFinalBlock) && (_mode == CryptoStreamMode.Write))
-				FlushFinalBlock ();
-
-			if (_stream != null)
-				_stream.Close ();
+			base.Close ();
 		}
 
 		public override int Read ([In,Out] byte[] buffer, int offset, int count)
@@ -353,6 +347,21 @@ namespace System.Security.Cryptography {
 		protected override void Dispose (bool disposing) 
 		{
 			if (!_disposed) {
+				if (disposing) {
+					// only flush in write mode (bugzilla 46143)
+					if (!_flushedFinalBlock) {
+						if (_mode == CryptoStreamMode.Write) {
+							FlushFinalBlock ();
+						} else {
+							// See bug #644648
+							_transform.TransformFinalBlock (new byte [0], 0, 0);
+						}
+						_flushedFinalBlock = true;
+					}
+
+					if (_stream != null)
+						_stream.Close ();
+				}
 				_disposed = true;
 				// always cleared for security reason
 				if (_workingBlock != null)
diff --git a/mcs/class/corlib/Test/System.Security.Cryptography/CryptoStreamTest.cs b/mcs/class/corlib/Test/System.Security.Cryptography/CryptoStreamTest.cs
index c4bfae156a5d6951f7664c322d1ca5a5a138e445..60746defc1cff1dba0ee6b0f3f54db9130733536 100644
--- a/mcs/class/corlib/Test/System.Security.Cryptography/CryptoStreamTest.cs
+++ b/mcs/class/corlib/Test/System.Security.Cryptography/CryptoStreamTest.cs
@@ -1389,6 +1389,46 @@ namespace MonoTests.System.Security.Cryptography {
 #endif
 		}
 
+		[Test]
+		public void ReadModeDispose_FinalBlock ()
+		{
+			using (SHA1 sha1 = SHA1.Create()) {
+				using (MemoryStream mem = new MemoryStream(new byte[] { 1, 2, 3 }, false))
+					using (CryptoStream cs = new CryptoStream(mem, sha1, CryptoStreamMode.Read))
+					{
+					}
+				byte b = sha1.Hash [0]; // This will throw if TransformFinalBlock not called in sha1
+				GC.KeepAlive (b); // just the warning...
+			}
+                }
+
+		[Test]
+		public void CustomDisposeCalled ()
+		{
+			using (MemoryStream mem = new MemoryStream(new byte[] { 1, 2, 3 }, false)) {
+				MyCryptoStream cs;
+				using (cs = new MyCryptoStream (mem, SHA1.Create()))
+				{
+				}
+				Assert.IsTrue (cs.DisposeCalled, "#1");
+			}
+		}
+
+		class MyCryptoStream : CryptoStream {
+			public bool DisposeCalled { get; private set;}
+
+			public MyCryptoStream(Stream stream, ICryptoTransform transform)
+						: base(stream, transform, CryptoStreamMode.Read)
+			{
+			}
+
+			protected override void Dispose(bool disposing)
+			{
+				base.Dispose(disposing);
+				DisposeCalled = true;
+			}
+		}
+
 		class ExpandTransform : ICryptoTransform {
 
 			public bool CanReuseTransform {