[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
{