diff --git a/RELNOTES b/RELNOTES
index c78f92c68977..d34c504ca760 100644
--- a/RELNOTES
+++ b/RELNOTES
@@ -10,6 +10,10 @@ newline.  Entries should be separated by a newline.
 
 Changes to this file should not be MFCed.
 
+r363679:
+	Applications using regex(3), e.g. sed/grep, will no longer accept
+	redundant escapes for most ordinary characters.
+
 r363253:
 	SCTP support has been removed from GENERIC kernel configurations.
 	The SCTP stack is now built as sctp.ko and can be dynamically loaded.
diff --git a/UPDATING b/UPDATING
index ee69605d9f28..be57064412b7 100644
--- a/UPDATING
+++ b/UPDATING
@@ -26,6 +26,13 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20200729:
+	r363679 has redefined some undefined behavior in regcomp(3); notably,
+	extraneous escapes of most ordinary characters will no longer be
+	accepted.  An exp-run has identified all of the problems with this in
+	ports, but other non-ports software may need extra escapes removed to
+	continue to function.
+
 20200627:
 	A new implementation of bc and dc has been imorted in r362681. This
 	implementation corrects non-conformant behavior of the previous bc