diff --git a/src/gsm/cbsp.c b/src/gsm/cbsp.c
index fa599c5..353f53f 100644
--- a/src/gsm/cbsp.c
+++ b/src/gsm/cbsp.c
@@ -130,13 +130,13 @@
 	if (secs <= 10)
 		return secs;
 	if (secs <= 30)
-		return (secs-10)/2;
+		return 10 + (secs-10)/2;
 	if (secs <= 120)
-		return (secs-30)/5;
+		return 30 + (secs-30)/5;
 	if (secs <= 600)
-		return (secs-120)/10;
+		return 120 + (secs-120)/10;
 	if (secs <= 60*60)
-		return (secs-600)/30;
+		return 600 + (secs-600)/30;
 	osmo_cbsp_errstr = "warning period out of range";
 	return -1;
 }