diff --git a/ion/pom.xml b/ion/pom.xml
index 786a78ea8..5fde8851c 100644
--- a/ion/pom.xml
+++ b/ion/pom.xml
@@ -52,7 +52,7 @@ tree model)
     <dependency>
       <groupId>com.amazon.ion</groupId>
       <artifactId>ion-java</artifactId>
-      <version>1.11.11</version>
+      <version>1.12.1</version>
     </dependency>
 
     <!-- will come from parent pom for later versions -->
diff --git a/release-notes/VERSION b/release-notes/VERSION
index 7d0e42a2a..90cf26f18 100644
--- a/release-notes/VERSION
+++ b/release-notes/VERSION
@@ -33,6 +33,9 @@ No changes since 3.1
 #785: (avro) Support `StreamReadConstraints.maxDocumentLength` and `maxTokenCount`
   in Avro parser
  (contributed by @pjfanning)
+#800: (ion) Upgrade `ion-java` dependency to 1.12.1 (from 1.11.11, which has
+  binary-write corruption bug)
+ (fix by @cowtowncoder, w/ Claude code)
 - Fixed signature of `CBORGenerator.writeNumberUnsigned()` methods
 
 3.1.6 (14-Aug-2026)