diff --git a/src/_zkapauthorizer/tests/test_plugin.py b/src/_zkapauthorizer/tests/test_plugin.py
index c4db72a340c1dc80fe78304925f0271281bbcf52..204b0554d94aec7b8ef2213440480f242ebaee5a 100644
--- a/src/_zkapauthorizer/tests/test_plugin.py
+++ b/src/_zkapauthorizer/tests/test_plugin.py
@@ -279,7 +279,7 @@ class ServerPluginTests(TestCase):
         metrics_path = self.useFixture(TempDir()).join(u"metrics")
         configuration = {
             u"prometheus-metrics-path": metrics_path,
-            u"prometheus-metrics-interval": str(metrics_interval.total_seconds()),
+            u"prometheus-metrics-interval": str(int(metrics_interval.total_seconds())),
             u"ristretto-issuer-root-url": "foo",
             u"ristretto-signing-key-path": SIGNING_KEY_PATH.path,
         }