diff --git a/bin/tests/system/rsabigexponent/README.md b/bin/tests/system/rsabigexponent/README.md
new file mode 100644
index 0000000000..4142221e45
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+++ b/bin/tests/system/rsabigexponent/README.md
@@ -0,0 +1,24 @@
+Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+
+See COPYRIGHT in the source root or https://isc.org/copyright.html for terms.
+
+The `rsabigexponent` test is used to `check max-rsa-exponent-size`.
+
+We only run this test on builds without PKCS#11, as we have control over
+the RSA exponent size with plain OpenSSL. We have not explored how to do
+this with PKCS#11, which would require generating such a key and then
+signing a zone with it. Additionally, even with control of the exponent
+size with PKCS#11, generating a DNSKEY with this property and signing
+such a zone would be slow and undesirable for each test run; instead, we
+use a pregenerated DNSKEY and a saved signed zone.  These are located in
+`rsabigexponent/ns2` and currently use RSASHA1 for the `DNSKEY`
+algorithm; however, that may need to be changed in the future.
+
+To generate the `DNSKEY` used in this test, we used `bigkey.c`, as
+dnssec-keygen is not capable of generating such keys.
+
+Do **not** remove `bigkey.c` as it may be needed to generate a new
+`DNSKEY` for testing purposes.
+
+`bigkey` is used to both test that we are not running under PKCS#11 and
+generate a `DNSKEY` key with a large RSA exponent.
diff --git a/util/copyrights b/util/copyrights
index 4898b95b77..f69380df2c 100644
--- a/util/copyrights
+++ b/util/copyrights
@@ -766,6 +766,7 @@
 ./bin/tests/system/rrsetorder/dig.out.random.good9	X	2006,2018,2019,2020,2021
 ./bin/tests/system/rrsetorder/setup.sh		SH	2018,2019,2020,2021
 ./bin/tests/system/rrsetorder/tests.sh		SH	2006,2007,2008,2011,2012,2014,2015,2016,2017,2018,2019,2020,2021
+./bin/tests/system/rsabigexponent/README.md	TXT.BRIEF	2021
 ./bin/tests/system/rsabigexponent/bigkey.c	C	2012,2014,2015,2016,2017,2018,2019,2020,2021
 ./bin/tests/system/rsabigexponent/clean.sh	SH	2012,2014,2016,2018,2019,2020,2021
 ./bin/tests/system/rsabigexponent/ns1/sign.sh	SH	2012,2014,2016,2018,2019,2020,2021