diff --git a/decor/eta.go b/decor/eta.go
index 3bb7fa1..5761617 100644
--- a/decor/eta.go
+++ b/decor/eta.go
@@ -21,6 +21,9 @@
 //
 //	`wcc` optional WC config
 func ETA(style int, age float64, sbCh chan time.Time, wcc ...WC) Decorator {
+	if sbCh == nil {
+		panic("start block channel must not be nil")
+	}
 	var wc WC
 	for _, widthConf := range wcc {
 		wc = widthConf
diff --git a/decor/speed.go b/decor/speed.go
index 01f6c2b..82afdcc 100644
--- a/decor/speed.go
+++ b/decor/speed.go
@@ -182,6 +182,9 @@
 }
 
 func speed(unit int, unitFormat string, age float64, sbCh chan time.Time, wcc ...WC) Decorator {
+	if sbCh == nil {
+		panic("start block channel must not be nil")
+	}
 	var wc WC
 	for _, widthConf := range wcc {
 		wc = widthConf