[csharp] Fix typo
diff --git a/csharp/src/Google.Protobuf/ByteString.cs b/csharp/src/Google.Protobuf/ByteString.cs
index 7ee157d..3eb00e5 100644
--- a/csharp/src/Google.Protobuf/ByteString.cs
+++ b/csharp/src/Google.Protobuf/ByteString.cs
@@ -55,7 +55,7 @@
         private readonly byte[] bytes;

 

         /// <summary>

-        /// Unsafe operations that can cause IO Failure and/or other catestrophic side-effects.

+        /// Unsafe operations that can cause IO Failure and/or other catastrophic side-effects.

         /// </summary>

         internal static class Unsafe

         {