diff --git a/src/test/unittest/unittest.sh b/src/test/unittest/unittest.sh
index d6b6e8502db..d9f44e1a87f 100644
--- a/src/test/unittest/unittest.sh
+++ b/src/test/unittest/unittest.sh
@@ -1765,6 +1765,9 @@ function require_mmap_under_valgrind() {
 		fatal "$FILE_MAX_DAX_DEVICES not found. Run make test."
 	fi
 
+	# XXX The number of device DAXes available under this condition is dependent
+	# on the size and the order of device DAXes in the testconfig.sh file.
+	# https://github.com/pmem/pmdk/issues/5615
 	if [ "$REQUIRE_DAX_DEVICES" -gt "$(< $FILE_MAX_DAX_DEVICES)" ]; then
 		msg "$UNITTEST_NAME: SKIP: anonymous mmap under Valgrind not possible for $REQUIRE_DAX_DEVICES DAX device(s)."
 		exit 0