diff --git a/repo-settings.c b/repo-settings.c
index 27f230681f..ab896fa84b 100644
--- a/repo-settings.c
+++ b/repo-settings.c
@@ -84,6 +84,8 @@ void prepare_repo_settings(struct repository *r)
 			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_NOOP;
 		else if (!strcasecmp(strval, "default"))
 			r->settings.fetch_negotiation_algorithm = FETCH_NEGOTIATION_DEFAULT;
+		else
+			die("unknown fetch negotiation algorithm '%s'", strval);
 	}
 
 	/*
diff --git a/t/t5500-fetch-pack.sh b/t/t5500-fetch-pack.sh
index bc29f03ce4..403d4e40a2 100755
--- a/t/t5500-fetch-pack.sh
+++ b/t/t5500-fetch-pack.sh
@@ -971,6 +971,13 @@ test_expect_success 'same as last but with config overrides' '
 		-c fetch.negotiationAlgorithm=default
 '
 
+test_expect_success 'ensure bogus fetch.negotiationAlgorithm yields error' '
+	test_when_finished rm -rf clientv0 &&
+	cp -r client clientv0 &&
+	test_must_fail git -C clientv0 --fetch.negotiationAlgorithm=bogus \
+		       fetch origin server_has both_have_2
+'
+
 test_expect_success 'filtering by size' '
 	rm -rf server client &&
 	test_create_repo server &&