diff --git a/UPGRADING b/UPGRADING
index 847b4a38477..c909884e166 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -468,7 +468,8 @@ JSON:
 
 PCRE:
   . The PCRE extension has been upgraded to PCRE2, which may cause minor
-    behavioral changes, and augments the existing regular expression syntax.
+    behavioral changes (for instance, character ranges in classes are now more
+    strictly interpreted), and augments the existing regular expression syntax.
     See <https://wiki.php.net/rfc/pcre2-migration> for details.
 
  Standard: