diff --git a/client.go b/client.go
index ccbf598..9b96b69 100644
--- a/client.go
+++ b/client.go
@@ -178,9 +178,15 @@ func (c *Client) Tick() {
 }
 
 func (c *Client) tick() {
-	// Batch: compute diff from accumulated actions.
+	// Only create a new state when the server has acked the previous one.
+	// This matches the Dart mosh client's behavior: at most one unacked
+	// state in flight. Keystrokes accumulate until the ack arrives, then
+	// the next tick sends them all as a single new state.
+	// Without this check, SetPending resets diffSent, causing Tick() to
+	// increment sentNum for the same cumulative payload — the server
+	// applies duplicate keystrokes.
 	c.actionsMu.Lock()
-	if c.dirty {
+	if c.dirty && c.transport.AckedByRemote() >= c.transport.SentNum() {
 		c.dirty = false
 		c.processAcksLocked()
 		newActions := c.actions[c.ackedActionCount:]
diff --git a/cmd/mosh-wasm/main.go b/cmd/mosh-wasm/main.go
index 5a33371..fe4289e 100644
--- a/cmd/mosh-wasm/main.go
+++ b/cmd/mosh-wasm/main.go
@@ -84,19 +84,12 @@ func newSession(url, key string) (*session, error) {
 func (s *session) jsObject() js.Value {
 	obj := js.Global().Get("Object").New()
 
-	// Tick immediately when idle (no unacked states). When busy (ack
-	// pending), queue keystrokes and let the interval flush them.
-	// This gives instant feel for the first key while preventing
-	// cumulative state duplication during rapid typing.
 	obj.Set("send", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		if len(args) < 1 {
 			return nil
 		}
 		s.client.Send([]byte(args[0].String()))
-		t := s.client.Transport()
-		if t.AckedByRemote() >= t.SentNum() {
-			s.client.Tick()
-		}
+		s.client.Tick()
 		return nil
 	}))
 
@@ -105,14 +98,11 @@ func (s *session) jsObject() js.Value {
 			return nil
 		}
 		s.client.Resize(uint16(args[0].Int()), uint16(args[1].Int()))
-		t := s.client.Transport()
-		if t.AckedByRemote() >= t.SentNum() {
-			s.client.Tick()
-		}
+		s.client.Tick()
 		return nil
 	}))
 
-	// tick() — send keepalive. Called by JS setInterval at a slow rate.
+	// tick() — flush pending keystrokes + keepalive/retransmit.
 	obj.Set("tick", js.FuncOf(func(this js.Value, args []js.Value) interface{} {
 		s.client.Tick()
 		return nil