diff --git a/docs/changelog/131950.yaml b/docs/changelog/131950.yaml
new file mode 100644
index 0000000000000..2df89d0f23b0d
--- /dev/null
+++ b/docs/changelog/131950.yaml
@@ -0,0 +1,5 @@
+pr: 131950
+summary: Fix encoding of non-ascii field names in ignored source
+area: Mapping
+type: bug
+issues: []
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapper.java
index d8d8200baac31..cd7f0d1c956dc 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapper.java
@@ -170,7 +170,7 @@ static byte[] encode(NameValue values) {
 
         byte[] nameBytes = values.name.getBytes(StandardCharsets.UTF_8);
         byte[] bytes = new byte[4 + nameBytes.length + values.value.length];
-        ByteUtils.writeIntLE(values.name.length() + PARENT_OFFSET_IN_NAME_OFFSET * values.parentOffset, bytes, 0);
+        ByteUtils.writeIntLE(nameBytes.length + PARENT_OFFSET_IN_NAME_OFFSET * values.parentOffset, bytes, 0);
         System.arraycopy(nameBytes, 0, bytes, 4, nameBytes.length);
         System.arraycopy(values.value.bytes, values.value.offset, bytes, 4 + nameBytes.length, values.value.length);
         return bytes;
diff --git a/server/src/test/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapperTests.java b/server/src/test/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapperTests.java
index 11e2305838705..423811c9e22a2 100644
--- a/server/src/test/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapperTests.java
+++ b/server/src/test/java/org/elasticsearch/index/mapper/IgnoredSourceFieldMapperTests.java
@@ -10,12 +10,14 @@
 package org.elasticsearch.index.mapper;
 
 import org.apache.lucene.index.DirectoryReader;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.CheckedConsumer;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.search.lookup.SourceFilter;
 import org.elasticsearch.test.FieldMaskingReader;
 import org.elasticsearch.xcontent.XContentBuilder;
+import org.elasticsearch.xcontent.json.JsonXContent;
 import org.hamcrest.Matchers;
 import org.junit.Before;
 
@@ -123,6 +125,15 @@ public void testIgnoredString() throws IOException {
         );
     }
 
+    public void testIgnoredStringFullUnicode() throws IOException {
+        String value = randomUnicodeOfCodepointLengthBetween(5, 20);
+        String fieldName = randomUnicodeOfCodepointLength(5);
+
+        String expected = Strings.toString(JsonXContent.contentBuilder().startObject().field(fieldName, value).endObject());
+
+        assertEquals(expected, getSyntheticSourceWithFieldLimit(b -> b.field(fieldName, value)));
+    }
+
     public void testIgnoredInt() throws IOException {
         int value = randomInt();
         assertEquals("{\"my_value\":" + value + "}", getSyntheticSourceWithFieldLimit(b -> b.field("my_value", value)));