diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 29c7d324ef0..2f87a5d9e0b 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -60,6 +60,10 @@ API Changes
 
 Improvements
 
+* LUCENE-9336: RegExp query now supports \w \W \d \D \s \S expressions.
+  This is a break with previous behaviour where these were (mis)interpreted
+  as literally the characters w W d etc. (Mark Harwood)
+
 * LUCENE-8757: When provided with an ExecutorService to run queries across
   multiple threads, IndexSearcher now groups small segments together, up to
   250k docs per slice. (Atri Sharma via Adrien Grand)
diff --git a/lucene/MIGRATE.md b/lucene/MIGRATE.md
index db188bed6ff..0956c8e0013 100644
--- a/lucene/MIGRATE.md
+++ b/lucene/MIGRATE.md
@@ -1,5 +1,9 @@
 # Apache Lucene Migration Guide
 
+## RegExp certain regular expressions now match differently (LUCENE-9336)
+
+The commonly used regular expressions \w \W \d \D \s and \S now work the same way [Java Pattern](https://docs.oracle.com/javase/tutorial/essential/regex/pre_char_classes.html#CHART) matching works. Previously these expressions were (mis)interpreted as searches for the literal characters w, d, s etc. 
+
 ## NGramFilterFactory "keepShortTerm" option was fixed to "preserveOriginal" (LUCENE-9259)
 
 The factory option name to output the original term was corrected in accordance with its Javadoc.