diff --git a/changelogs/4.21.md b/changelogs/4.21.md
index 34254d6b2..da4cc78c0 100644
--- a/changelogs/4.21.md
+++ b/changelogs/4.21.md
@@ -69,3 +69,9 @@ Released 17th May 2023.
 - Registered but ineligible ticking chunks are no longer rechecked every tick.
     - This was causing wasted cycles during async worker backlog.
     - The internal system must call `markTickingChunkForRecheck()` whenever a ticking chunk's eligibility for ticking has potentially changed, rather than just when it has changed from a yes to a no.
+
+# 4.21.1
+Released 30th May 2023.
+
+## Fixes
+- Fixed server crash due to a bug in upstream dependency [`netresearch/jsonmapper`](https://github.com/cweiske/JsonMapper).
diff --git a/src/VersionInfo.php b/src/VersionInfo.php
index ea1082c12..4dd279578 100644
--- a/src/VersionInfo.php
+++ b/src/VersionInfo.php
@@ -32,7 +32,7 @@ use function str_repeat;
 final class VersionInfo{
 	public const NAME = "PocketMine-MP";
 	public const BASE_VERSION = "4.21.1";
-	public const IS_DEVELOPMENT_BUILD = true;
+	public const IS_DEVELOPMENT_BUILD = false;
 	public const BUILD_CHANNEL = "stable";
 
 	private function __construct(){