diff --git a/command.go b/command.go
index 41fde30..992197a 100644
--- a/command.go
+++ b/command.go
@@ -146,6 +146,10 @@ func (cmd *baseCmd) setErr(e error) {
 }
 
 func newBaseCmd(args []interface{}) baseCmd {
+	if len(args) > 0 {
+		// Cmd name is expected to be in lower case.
+		args[0] = internal.ToLower(args[0].(string))
+	}
 	return baseCmd{_args: args}
 }
 
diff --git a/internal/util.go b/internal/util.go
new file mode 100644
index 0000000..5986cc5
--- /dev/null
+++ b/internal/util.go
@@ -0,0 +1,27 @@
+package internal
+
+func ToLower(s string) string {
+	if isLower(s) {
+		return s
+	}
+
+	b := make([]byte, len(s))
+	for i := range b {
+		c := s[i]
+		if c >= 'A' && c <= 'Z' {
+			c += 'a' - 'A'
+		}
+		b[i] = c
+	}
+	return string(b)
+}
+
+func isLower(s string) bool {
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c >= 'A' && c <= 'Z' {
+			return false
+		}
+	}
+	return true
+}