diff --git a/csharp/src/Google.Protobuf.Test/SampleNaNs.cs b/csharp/src/Google.Protobuf.Test/SampleNaNs.cs
new file mode 100644
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+++ b/csharp/src/Google.Protobuf.Test/SampleNaNs.cs
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+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2017 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Samples of different not-a-number values, for testing equality comparisons.
+    /// </summary>
+    public static class SampleNaNs
+    {
+        public static double Regular { get; } = double.NaN;
+
+        // Signalling bit is inverted compared with double.NaN. Doesn't really matter
+        // whether that makes it quiet or signalling - it's different.
+        public static double SignallingFlipped { get; } = 
+            BitConverter.Int64BitsToDouble(BitConverter.DoubleToInt64Bits(double.NaN) ^ -0x8000_0000_0000_0000L);
+
+        // A bit in the middle of the mantissa is flipped; this difference is preserved when casting to float.
+        public static double PayloadFlipped { get; } =
+            BitConverter.Int64BitsToDouble(BitConverter.DoubleToInt64Bits(double.NaN) ^ 0x1_0000_0000L);
+    }
+}