diff --git a/builtin.go b/builtin.go
index 5257ffb..35706b4 100644
--- a/builtin.go
+++ b/builtin.go
@@ -17,8 +17,8 @@ import (
 func (c *Client) registerBuiltins() {
 	c.debug.Print("registering built-in handlers")
 
-	c.mu.Lock()
-	defer c.mu.Unlock()
+	c.Handlers.mu.Lock()
+	defer c.Handlers.mu.Unlock()
 
 	// Built-in things that should always be supported.
 	c.Handlers.register(true, true, RPL_WELCOME, HandlerFunc(handleConnect))
diff --git a/handler.go b/handler.go
index fce8f29..b543300 100644
--- a/handler.go
+++ b/handler.go
@@ -214,6 +214,8 @@ type execStack struct {
 // Please note that there is no specific order/priority for which the handlers
 // are executed.
 func (c *Caller) exec(command string, bg bool, client *Client, event *Event) {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 
 	// Build a stack of handlers which can be executed concurrently.
 	var stack []execStack