diff --git a/libosmocore/include/osmocore/rate_ctr.h b/libosmocore/include/osmocore/rate_ctr.h
index c6a1ace..88c9de5 100644
--- a/libosmocore/include/osmocore/rate_ctr.h
+++ b/libosmocore/include/osmocore/rate_ctr.h
@@ -33,8 +33,8 @@
 
 /* Describe a counter group class */
 struct rate_ctr_group_desc {
-	/* The prefix / format string to be used for all counters */
-	char *group_prefix_fmt;
+	/* The prefix to the name of all counters in this group */
+	char *group_name_prefix;
 	/* The human-readable description of the group */
 	char *group_description;
 	/* The number of counters in this group */
@@ -49,8 +49,8 @@
 	struct llist_head list;
 	/* Pointer to the counter group class */
 	const struct rate_ctr_group_desc *desc;
-	/* The name prefix generated from desc->group_prefix_fmt and index */
-	char *name_prefix;
+	/* The index of this ctr_group within its class */
+	unsigned int idx;
 	/* Actual counter structures below */
 	struct rate_ctr ctr[0];
 };
diff --git a/libosmocore/src/rate_ctr.c b/libosmocore/src/rate_ctr.c
index 9b2459e..e48c779 100644
--- a/libosmocore/src/rate_ctr.c
+++ b/libosmocore/src/rate_ctr.c
@@ -51,9 +51,7 @@
 		return NULL;
 
 	group->desc = desc;
-	/* Generate the Group prefix from the user-specified index */
-	group->name_prefix = talloc_size(group, strlen(desc->group_prefix_fmt) + 20);
-	sprintf(group->name_prefix, desc->group_prefix_fmt, idx);
+	group->idx = idx;
 
 	llist_add(&group->list, &rate_ctr_groups);