diff --git a/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst b/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst
new file mode 100644
index 00000000000000..69b9de1beae0d1
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2020-05-28-06-06-47.bpo-40791.QGZClX.rst
@@ -0,0 +1 @@
+Add ``volatile`` to the accumulator variable in ``hmac.compare_digest``, making constant-time-defeating optimizations less likely.
\ No newline at end of file
diff --git a/Modules/_operator.c b/Modules/_operator.c
index 51daa1ff6cfb30..7fff654ca610be 100644
--- a/Modules/_operator.c
+++ b/Modules/_operator.c
@@ -735,7 +735,7 @@ _tscmp(const unsigned char *a, const unsigned char *b,
volatile const unsigned char *left;
volatile const unsigned char *right;
Py_ssize_t i;
- unsigned char result;
+ volatile unsigned char result;
/* loop count depends on length of b */
length = len_b;
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