diff --git a/io/key/key.go b/io/key/key.go
index 8b11caf7..8d951d9f 100644
--- a/io/key/key.go
+++ b/io/key/key.go
@@ -121,6 +121,9 @@ func (m Modifiers) Contain(m2 Modifiers) bool {
 }
 
 func (h InputOp) Add(o *op.Ops) {
+	if h.Tag == nil {
+		panic("Tag must be non-nil")
+	}
 	data := o.Write1(opconst.TypeKeyInputLen, h.Tag)
 	data[0] = byte(opconst.TypeKeyInput)
 }
diff --git a/io/pointer/pointer.go b/io/pointer/pointer.go
index 9e054fbc..b112bfde 100644
--- a/io/pointer/pointer.go
+++ b/io/pointer/pointer.go
@@ -189,6 +189,9 @@ func (op CursorNameOp) Add(o *op.Ops) {
 }
 
 func (h InputOp) Add(o *op.Ops) {
+	if h.Tag == nil {
+		panic("Tag must be non-nil")
+	}
 	data := o.Write1(opconst.TypePointerInputLen, h.Tag)
 	data[0] = byte(opconst.TypePointerInput)
 	if h.Grab {