diff --git a/tests/conftest.py b/tests/conftest.py
index e222642..1952ec1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -13,7 +13,7 @@
 
 
 def pytest_report_header(config):
-    return "OpenSSL: {}".format(openssl_backend.openssl_version_text())
+    return "OpenSSL: {0}".format(openssl_backend.openssl_version_text())
 
 
 def pytest_generate_tests(metafunc):