diff --git a/test/filter_plugin.c b/test/filter_plugin.c
index 86f24eee973..2347f38bfe2 100644
--- a/test/filter_plugin.c
+++ b/test/filter_plugin.c
@@ -849,7 +849,7 @@ test_creating_groups_using_plugins(hid_t fid)
     for (i = 0; i < N_SUBGROUPS; i++) {
         char *sp = subgroup_name;
 
-        sp += snprintf(subgroup_name, sizeof(subgroup_name), SUBGROUP_PREFIX "%d");
+        sp += snprintf(subgroup_name, sizeof(subgroup_name), SUBGROUP_PREFIX "%d", i);
 
         if ((sub_gid = H5Gcreate2(gid, subgroup_name, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT)) < 0)
             TEST_ERROR;
@@ -907,7 +907,7 @@ test_opening_groups_using_plugins(hid_t fid)
     for (i = 0; i < N_SUBGROUPS; i++) {
         char *sp = subgroup_name;
 
-        sp += snprintf(subgroup_name, sizeof(subgroup_name), SUBGROUP_PREFIX "%d");
+        sp += snprintf(subgroup_name, sizeof(subgroup_name), SUBGROUP_PREFIX "%d", i);
 
         if ((sub_gid = H5Gopen2(gid, subgroup_name, H5P_DEFAULT)) < 0)
             TEST_ERROR;