diff --git a/include/haproxy/tinfo-t.h b/include/haproxy/tinfo-t.h
index bbba5a1db..5f0d79426 100644
--- a/include/haproxy/tinfo-t.h
+++ b/include/haproxy/tinfo-t.h
@@ -54,7 +54,7 @@ enum {
 struct tgroup_info {
 	uint base;                 /* first thread in this group */
 	uint count;                /* number of threads in this group */
-	uint tgid;                 /* group ID (starts at 1, 0=unspecified) */
+	ulong tgid_bit;            /* bit corresponding to the tgroup ID */
 
 	/* pad to cache line (64B) */
 	char __pad[0];            /* unused except to check remaining room */
diff --git a/src/thread.c b/src/thread.c
index c5f06038f..dedde13b4 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -1019,7 +1019,7 @@ int thread_map_to_groups()
 	for (g = 0; g < global.nbtgroups; g++) {
 		if (!ha_tgroup_info[g].count)
 			ug++;
-		ha_tgroup_info[g].tgid = g + 1;
+		ha_tgroup_info[g].tgid_bit = 1UL << g;
 	}
 
 	if (ug > ut) {