diff --git a/testing/external/subdir-btest.cfg b/testing/external/subdir-btest.cfg
index 20c8500948..9c7a1e2f5e 100644
--- a/testing/external/subdir-btest.cfg
+++ b/testing/external/subdir-btest.cfg
@@ -25,4 +25,6 @@ BUILD=%(testbase)s/../../../%(build_dir)s
 ZEEK_DNS_FAKE=1
 # Fedora/CentOS/RedHat have MD5 disabled for certificate verification and need setting an environment variable to permit it:
 OPENSSL_ENABLE_MD5_VERIFY=1
+# Fedora/RedHat have SHA1 disabled for certificate verification and need setting an environment variable to permit it:
+OPENSSL_ENABLE_SHA1_SIGNATURES=1
 UBSAN_OPTIONS=print_stacktrace=1