diff --git a/command/builder.go b/command/builder.go
index 5c9b4de..c0782c6 100644
--- a/command/builder.go
+++ b/command/builder.go
@@ -7,8 +7,10 @@ import (
 )
 
 // New initialises a root Node.
-func New(output io.Writer, logf LogFunc, name string) Command {
-	return rootNode{newNode(output, logf, name, "")}
+func New(output io.Writer, logf LogFunc, name string, early HandlerFunc) Command {
+	c := rootNode{newNode(output, logf, name, "")}
+	c.f = early
+	return c
 }
 
 func newNode(output io.Writer, logf LogFunc, name, usage string) *node {
diff --git a/command/builder_test.go b/command/builder_test.go
index 1cd4ce3..22ce7ae 100644
--- a/command/builder_test.go
+++ b/command/builder_test.go
@@ -7,7 +7,7 @@ import (
 )
 
 func TestBuild(t *testing.T) {
-	c := command.New(nil, nil, "test")
+	c := command.New(nil, nil, "test", nil)
 	stubHandler := func([]string) error { panic("unreachable") }
 
 	t.Run("nil direct handler", func(t *testing.T) {
diff --git a/command/parse.go b/command/parse.go
index 6081ca6..0212046 100644
--- a/command/parse.go
+++ b/command/parse.go
@@ -34,9 +34,6 @@ func (n *node) Parse(arguments []string) error {
 
 match:
 	if n.child != nil {
-		if n.f != nil {
-			panic("invalid subcommand tree state")
-		}
 		// propagate help prefix early: flag set usage dereferences help
 		n.child.prefix = append(n.prefix, n.name)
 	}
@@ -50,6 +47,17 @@ match:
 	args := n.set.Args()
 
 	if n.child != nil {
+		if n.f != nil {
+			if n.usage != "" { // root node early special case
+				panic("invalid subcommand tree state")
+			}
+
+			// special case: root node calls HandlerFunc for initialisation
+			if err := n.f(nil); err != nil {
+				return err
+			}
+		}
+
 		if len(args) == 0 {
 			return n.writeHelp()
 		}
diff --git a/command/parse_test.go b/command/parse_test.go
index f424e97..3174dcc 100644
--- a/command/parse_test.go
+++ b/command/parse_test.go
@@ -24,13 +24,13 @@ func TestParse(t *testing.T) {
 	}{
 		{
 			"d=0 empty sub",
-			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root") },
+			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root", nil) },
 			[]string{""},
 			"", "test: \"root\" has no subcommands\n", command.ErrEmptyTree,
 		},
 		{
 			"d=0 empty sub garbage",
-			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root") },
+			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root", nil) },
 			[]string{"a", "b", "c", "d"},
 			"", "test: \"root\" has no subcommands\n", command.ErrEmptyTree,
 		},
@@ -77,6 +77,18 @@ func TestParse(t *testing.T) {
 			"flag provided but not defined: -val\n\nUsage:\ttest flag [-h | --help] COMMAND [OPTIONS]\n\n", "",
 			errors.New("flag provided but not defined: -val"),
 		},
+		{
+			"d=0 bool flag",
+			buildTestCommand,
+			[]string{"-v", "succeed"},
+			"", "test: verbose\n", nil,
+		},
+		{
+			"d=0 bool flag early error",
+			buildTestCommand,
+			[]string{"--fail", "succeed"},
+			"", "", errSuccess,
+		},
 
 		{
 			"d=1 empty sub",
@@ -126,7 +138,7 @@ func TestParse(t *testing.T) {
 			buildTestCommand,
 			[]string{},
 			`
-Usage:	test [-h | --help] [-v] [--val <value>] COMMAND [OPTIONS]
+Usage:	test [-h | --help] [-v] [--fail] [--val <value>] COMMAND [OPTIONS]
 
 Commands:
     error      return an error
@@ -144,7 +156,7 @@ Commands:
 			buildTestCommand,
 			[]string{"-h"},
 			`
-Usage:	test [-h | --help] [-v] [--val <value>] COMMAND [OPTIONS]
+Usage:	test [-h | --help] [-v] [--fail] [--val <value>] COMMAND [OPTIONS]
 
 Commands:
     error      return an error
@@ -156,7 +168,9 @@ Commands:
     deep       top level of command tree with various levels
 
 Flags:
-  -v	verbosity
+  -fail
+    	fail early
+  -v	verbose output
   -val string
     	store val for the "flag" command (default "default")
 
@@ -239,11 +253,24 @@ var (
 )
 
 func buildTestCommand(wout, wlog io.Writer) (c command.Command) {
-	var val string
+	var (
+		flagVerbose bool
+		flagFail    bool
+		flagVal     string
+	)
 
 	logf := newLogFunc(wlog)
-	c = command.New(wout, logf, "test").
-		Flag(new(bool), "v", command.BoolFlag(false), "verbosity").
+	c = command.New(wout, logf, "test", func([]string) error {
+		if flagVerbose {
+			logf("verbose")
+		}
+		if flagFail {
+			return errSuccess
+		}
+		return nil
+	}).
+		Flag(&flagVerbose, "v", command.BoolFlag(false), "verbose output").
+		Flag(&flagFail, "fail", command.BoolFlag(false), "fail early").
 		Command("error", "return an error", func([]string) error {
 			return errSuccess
 		}).
@@ -255,9 +282,9 @@ func buildTestCommand(wout, wlog io.Writer) (c command.Command) {
 			_, err := fmt.Fprint(wout, a...)
 			return err
 		}).
-		Flag(&val, "val", command.StringFlag("default"), "store val for the \"flag\" command").
+		Flag(&flagVal, "val", command.StringFlag("default"), "store val for the \"flag\" command").
 		Command("flag", "print value passed by flag", func(args []string) error {
-			_, err := fmt.Fprint(wout, val)
+			_, err := fmt.Fprint(wout, flagVal)
 			return err
 		})
 
diff --git a/command/unreachable_test.go b/command/unreachable_test.go
index 9ace479..7140818 100644
--- a/command/unreachable_test.go
+++ b/command/unreachable_test.go
@@ -24,10 +24,10 @@ func TestParseUnreachable(t *testing.T) {
 	// a node with descendents must not have a direct handler
 	t.Run("sub handle conflict", func(t *testing.T) {
 		defer checkRecover(t, "Parse", "invalid subcommand tree state")
-		n := newNode(panicWriter{}, nil, " ", "")
+		n := newNode(panicWriter{}, nil, " ", " ")
 		n.adopt(newNode(panicWriter{}, nil, " ", " "))
 		n.f = func([]string) error { panic("unreachable") }
-		_ = n.Parse(nil)
+		_ = n.Parse([]string{" "})
 	})
 
 	// this would only happen if a node was matched twice