diff --git a/CHANGELOG.md b/CHANGELOG.md
index e8eb99ff87..13f6311b32 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,20 @@ tag versions. The Bond compiler (`gbc`) and
 different versioning scheme, following the Haskell community's
 [package versioning policy](https://wiki.haskell.org/Package_versioning_policy).
 
+## Unreleased ##
+
+* IDL core version: TBD
+* C++ version: TBD
+* C# NuGet version: bug fix bump needed
+* `gbc` & compiler library: TBD
+
+### C# ###
+
+* Fixed a performance regression in `OutputBuffer.Grow`: it was incorrectly
+  growing the buffer by one byte at a time instead of geometrically. ([Issue
+  \#1065](https://github.com/microsoft/bond/issues/1065), [Pull request
+  \#1066](https://github.com/microsoft/bond/pull/1066))
+
 ## 9.0.2: 2020-08-03 ##
 * IDL core version: 3.0
 * C++ version: 9.0.2
diff --git a/cs/src/core/io/safe/OutputBuffer.cs b/cs/src/core/io/safe/OutputBuffer.cs
index 7ad470042f..1fd83138c7 100644
--- a/cs/src/core/io/safe/OutputBuffer.cs
+++ b/cs/src/core/io/safe/OutputBuffer.cs
@@ -221,7 +221,7 @@ public virtual void WriteString(Encoding encoding, string value, int size)
         internal virtual void Grow(int count)
         {
             int minLength = checked(position + count);
-            length = checked(length + length >> 1);
+            length = checked(length + (length >> 1));
 
             const int ArrayIndexMaxValue = 0x7FFFFFC7;
             if ((uint)length > ArrayIndexMaxValue)