diff --git a/builds/install/misc/firebird.conf b/builds/install/misc/firebird.conf
index a4208dca8d..431d9cc11b 100644
--- a/builds/install/misc/firebird.conf
+++ b/builds/install/misc/firebird.conf
@@ -503,6 +503,26 @@
 #OuterJoinConversion = true
 
 
+# ----------------------------
+# Defines whether subqueries inside IN/EXISTS predicates are attempted to be merged
+# with the outer query and converted into semi-joins, if possible.
+#
+# Being an experimental feature, it's disabled by default.
+# Enable to give it a try for a possibly better performance due to subquery being
+# evaluated just once and then cached.
+#
+# CAUTION!
+# There is no guarantee that this setting will be available in future Firebird
+# versions. Once this feature is proved to be superior in most use cases,
+# this setting will be removed and this conversion will become unconditional.
+#
+# Per-database configurable.
+#
+# Type: boolean
+#
+#SubQueryConversion = false
+
+
 # ============================
 # Plugin settings
 # ============================