# Lowercase normalizer and backslash in 8.19.x

**URL:** <https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494>\
**Category:** Elastic Search\
**Created:** [September 1, 2025, 3:26pm UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494 "2025-09-01T15:26:22Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![MikeSER](https://avatars.discourse-cdn.com/v4/letter/m/839c29/32.png) [@MikeSER](https://discuss.elastic.co/u/MikeSER)\
**Post date:** [September 1, 2025, 3:26pm UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494/1 "2025-09-01T15:26:22Z")

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I have a field defined as such:

`"myfield": { `[`-`](http://localhost:9000/#)` `  
` "type": "keyword",`  
` "store": true,`  
` "fields": {`[`-`](http://localhost:9000/#)` `  
` "lowercase": {`[`-`](http://localhost:9000/#)` `  
` "type": "keyword",`  
` "normalizer": "lowercase"`  
` }`  
` }`  
` },`

this stores the value in the original case and additionally a lower case variant. The lower case variant is created by Elasticsearch while storing/changing the document.

A value `“AbC\\dEf”` is stored as `“abc\\def”` in the lowercase sub-field (note this is in JSON notation, where a backslash mask a special character; so in reality there is only one backslash).

This worked till 8.18.5.

In 8.19.0 - 8.19.2 it stores the value as `“abc\\\\def”` and the value can’t be found anymore when I search with `“abc\\def”`.

Is this an intended behavior?

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<div class="post-metadata">

**Author:** ![MikeSER](https://avatars.discourse-cdn.com/v4/letter/m/839c29/32.png) [@MikeSER](https://discuss.elastic.co/u/MikeSER)\
**Post date:** [September 1, 2025, 4:22pm UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494/2 "2025-09-01T16:22:00Z")

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Just checked: It works in 8.18.5 and lower and 9.0.5.

It doesn’t work (means doubled backslashes) in 8.19.0-8.19.2 and 9.1.2.

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**Author:** ![Kathleen\_DeRusso](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/kathleen_derusso/32/132039_2.png) [@Kathleen\_DeRusso](https://discuss.elastic.co/u/Kathleen_DeRusso)\
**Post date:** [September 2, 2025, 12:44pm UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494/3 "2025-09-02T12:44:27Z")

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Hi, thanks for reporting. That sounds like a bug, would you greatly mind opening an issue at [https://github.com/elastic/elasticsearch/issues](https://github.com/elastic/elasticsearch/issues)?

Thanks!

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<div class="post-metadata">

**Author:** ![MikeSER](https://avatars.discourse-cdn.com/v4/letter/m/839c29/32.png) [@MikeSER](https://discuss.elastic.co/u/MikeSER)\
**Post date:** [September 3, 2025, 5:48am UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494/4 "2025-09-03T05:48:53Z")

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> [@MikeSER](#):
>
> `"myfield": { ` [`-`](http://localhost:9000/#)` `  
> ` "type": "keyword",`  
> ` "store": true,`  
> ` "fields": {` [`-`](http://localhost:9000/#)` `  
> ` "lowercase": {` [`-`](http://localhost:9000/#)` `  
> ` "type": "keyword",`  
> ` "normalizer": "lowercase"`  
> ` }`  
> ` }`  
> ` },`

Created an issue: [lowercase normalizer doubles backslashes in 8.19.x and 9.1.x · Issue #134023 · elastic/elasticsearch · GitHub](https://github.com/elastic/elasticsearch/issues/134023)

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<div class="post-metadata">

**Author:** ![Kathleen\_DeRusso](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/kathleen_derusso/32/132039_2.png) [@Kathleen\_DeRusso](https://discuss.elastic.co/u/Kathleen_DeRusso)\
**Post date:** [September 3, 2025, 12:08pm UTC](https://discuss.elastic.co/t/lowercase-normalizer-and-backslash-in-8-19-x/381494/5 "2025-09-03T12:08:19Z")

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Thank you! We’ll get it triaged to the right team. Appreciate you finding it and logging the bug!