diff --git a/ion/src/main/java/com/fasterxml/jackson/dataformat/ion/ionvalue/TimestampSerializer.java b/ion/src/main/java/com/fasterxml/jackson/dataformat/ion/ionvalue/TimestampSerializer.java
index 4fbd1aa07..a90ec490f 100644
--- a/ion/src/main/java/com/fasterxml/jackson/dataformat/ion/ionvalue/TimestampSerializer.java
+++ b/ion/src/main/java/com/fasterxml/jackson/dataformat/ion/ionvalue/TimestampSerializer.java
@@ -35,8 +35,12 @@ protected TimestampSerializer() {
     }
 
     @Override
-    public void serialize(Timestamp value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
-        IonGenerator joiGenerator = (IonGenerator) jgen;
-        joiGenerator.writeValue(value);
+    public void serialize(Timestamp value, JsonGenerator g, SerializerProvider provider) throws IOException {
+        if (g instanceof IonGenerator) {
+            ((IonGenerator) g).writeValue(value);
+        } else {
+            // Otherwise probably `TokenBuffer`, so
+            g.writeEmbeddedObject(value);
+        }
     }
 }
diff --git a/ion/src/test/java/com/fasterxml/jackson/dataformat/ion/failing/IonTimestampDeser251Test.java b/ion/src/test/java/com/fasterxml/jackson/dataformat/ion/IonTimestampDeser251Test.java
similarity index 50%
rename from ion/src/test/java/com/fasterxml/jackson/dataformat/ion/failing/IonTimestampDeser251Test.java
rename to ion/src/test/java/com/fasterxml/jackson/dataformat/ion/IonTimestampDeser251Test.java
index a06fab028..06b9578da 100644
--- a/ion/src/test/java/com/fasterxml/jackson/dataformat/ion/failing/IonTimestampDeser251Test.java
+++ b/ion/src/test/java/com/fasterxml/jackson/dataformat/ion/IonTimestampDeser251Test.java
@@ -1,7 +1,8 @@
-package com.fasterxml.jackson.dataformat.ion.failing;
+package com.fasterxml.jackson.dataformat.ion;
 
 import org.junit.Test;
 
+import com.amazon.ion.Timestamp;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.DeserializationFeature;
@@ -15,12 +16,30 @@
 // For [dataformats-binary#251]
 public class IonTimestampDeser251Test
 {
-    static class Message {
+    static class MessageWithoutTimestamp {
         final String message;
         final Integer count;
 
         @JsonCreator
-        public Message(@JsonProperty("message") String message,
+        public MessageWithoutTimestamp(@JsonProperty("message") String message,
+                       @JsonProperty("count") Integer count) {
+            this.message = message;
+            this.count = count;
+        }
+
+        public String getMessage() {
+            return message;
+        }
+    }
+
+    static class MessageWithTimestamp {
+        final String message;
+        final Integer count;
+
+        public Timestamp timestamp;
+
+        @JsonCreator
+        public MessageWithTimestamp(@JsonProperty("message") String message,
                        @JsonProperty("count") Integer count) {
             this.message = message;
             this.count = count;
@@ -38,10 +57,21 @@ public String getMessage() {
 
     // [dataformats-binary#251]
     @Test
-    public void testTimestampDeserWithBuffering() throws Exception {
+    public void testDeserWithIgnoredBufferedTimestamp() throws Exception {
+        String ion = "{message: \"Hello, world\", timestamp:2021-03-10T01:49:30.242-00:00}";
+        MessageWithoutTimestamp message = ION_MAPPER.readValue(ion,
+                MessageWithoutTimestamp.class);
+        assertNotNull(message);
+        assertEquals("Hello, world", message.message);
+    }
+
+    @Test
+    public void testDeserWithBufferedTimestamp() throws Exception {
         String ion = "{message: \"Hello, world\", timestamp:2021-03-10T01:49:30.242-00:00}";
-        Message message = ION_MAPPER.readValue(ion, Message.class);
+        MessageWithTimestamp message = ION_MAPPER.readValue(ion,
+                MessageWithTimestamp.class);
         assertNotNull(message);
         assertEquals("Hello, world", message.message);
+        assertNotNull(message.timestamp);
     }
 }
diff --git a/release-notes/VERSION-2.x b/release-notes/VERSION-2.x
index fb2b57f8d..41472b95a 100644
--- a/release-notes/VERSION-2.x
+++ b/release-notes/VERSION-2.x
@@ -16,6 +16,8 @@ Active maintainers:
 
 2.17.0 (not yet released)
 
+#251 (ion) Unable to deserialize Object with unknown `Timestamp` field
+ (reported by @mgoertzen)
 #316 (cbor) Uncaught exception in
   `com.fasterxml.jackson.dataformat.cbor.CBORParser._finishShortText`
 #392: (cbor, smile) Support `StreamReadConstraints.maxDocumentLength`