diff --git a/configure/RULES.Db b/configure/RULES.Db
index 46d3ad223..fbd7aab72 100644
--- a/configure/RULES.Db
+++ b/configure/RULES.Db
@@ -8,6 +8,9 @@
 #*************************************************************************
 #RULES.Db
 
+# Set db substitutions file suffix
+SUBST_SUFFIX ?= .substitutions
+
 #####################################################  vpath
 
 vpath %.dbd $(USR_VPATH) $(SRC_DIRS) $(dir $(DBD))
@@ -45,8 +48,6 @@ DBD += $(foreach type, $(CROSS_TARGET_OS_TYPES), $(DBD_$(type)))
 #
 # ---------------------------------------------------
 
-SUBST_SUFFIX ?= .substitutions
-
 DBDINC_NAME = $(patsubst %.h,%,$(patsubst %.dbd,%,$(DBDINC)))
 DBD += $(addsuffix .dbd,$(DBDINC_NAME))
 INC += $(addsuffix .h,$(DBDINC_NAME))
diff --git a/documentation/RELEASE_NOTES.html b/documentation/RELEASE_NOTES.html
index 6247f5dc7..6d686e3ed 100644
--- a/documentation/RELEASE_NOTES.html
+++ b/documentation/RELEASE_NOTES.html
@@ -15,6 +15,10 @@ EPICS Base 3.15.0.x releases are not intended for use in production systems.</p>
 <h2 align="center">Changes between 3.15.0.1 and 3.15.0.2</h2>
 <!-- Insert new items immediately below here ... -->
 
+<h3>User specified db substitution file suffix</h3>
+
+<p>Per Dirk Zimoch's suggestion, a user specified db substitution file suffix is now allowed by setting the variable SUBST_SUFFIX in a configuration directory CONFIG_SITE file or in a Makefile before the include $(TOP)/configure/RULES line. The default is SUBST_SUFFIX=.substitutions.</p>
+
 <h3>NTP Time Provider adjusts to OS tick rate changes</h3>
 
 <p>Dirk Zimoch provided code that allows the NTP Time provider (used on VxWorks