diff --git a/char.go b/char.go
index 9a74523..2f2728a 100644
--- a/char.go
+++ b/char.go
@@ -23,10 +23,11 @@ func newChar(
 	}
 }
 
-func (p *charParser) nodeName() string       { return p.name }
-func (p *charParser) nodeID() int            { return p.id }
-func (p *charParser) setID(id int)           { p.id = id }
-func (p *charParser) commitType() CommitType { return Alias }
+func (p *charParser) nodeName() string                  { return p.name }
+func (p *charParser) nodeID() int                       { return p.id }
+func (p *charParser) setID(id int)                      { p.id = id }
+func (p *charParser) commitType() CommitType            { return Alias }
+func (p *charParser) normalize(*registry, *idSet) error { return nil }
 
 func (p *charParser) init(r *registry) error { return nil }
 
diff --git a/choice.go b/choice.go
index 4cc37f6..57a41f1 100644
--- a/choice.go
+++ b/choice.go
@@ -38,6 +38,24 @@ func (d *choiceDefinition) nodeID() int            { return d.id }
 func (d *choiceDefinition) setID(id int)           { d.id = id }
 func (d *choiceDefinition) commitType() CommitType { return d.commit }
 
+func (d *choiceDefinition) normalize(r *registry, path *idSet) error {
+	if path.has(d.id) {
+		return nil
+	}
+
+	path.set(d.id)
+	for i := range d.elements {
+		element, ok := r.definition(d.elements[i])
+		if !ok {
+			return parserNotFound(d.elements[i])
+		}
+
+		element.normalize(r, path)
+	}
+
+	return nil
+}
+
 func (d *choiceDefinition) init(r *registry) error {
 	if d.cbuilder == nil {
 		d.cbuilder = &choiceBuilder{
diff --git a/parse.go b/parse.go
index 958b505..cec0809 100644
--- a/parse.go
+++ b/parse.go
@@ -7,6 +7,7 @@ type definition interface {
 	nodeID() int
 	commitType() CommitType
 	setID(int)
+	normalize(*registry, *idSet) error
 	init(*registry) error
 	setIncludedBy(*registry, int, *idSet) error
 	parser(*registry, *idSet) (parser, error)
diff --git a/sequence.go b/sequence.go
index 03e4fcd..d133ca0 100644
--- a/sequence.go
+++ b/sequence.go
@@ -44,6 +44,24 @@ func (d *sequenceDefinition) nodeID() int            { return d.id }
 func (d *sequenceDefinition) setID(id int)           { d.id = id }
 func (d *sequenceDefinition) commitType() CommitType { return d.commit }
 
+func (d *sequenceDefinition) normalize(r *registry, path *idSet) error {
+	if path.has(d.id) {
+		return nil
+	}
+
+	path.set(d.id)
+	for i := range d.items {
+		element, ok := r.definition(d.items[i].Name)
+		if !ok {
+			return parserNotFound(d.items[i].Name)
+		}
+
+		element.normalize(r, path)
+	}
+
+	return nil
+}
+
 func (d *sequenceDefinition) includeItems() bool {
 	return len(d.items) == 1 && d.items[0].Min == 1 && d.items[0].Max == 1
 }
diff --git a/syntax.go b/syntax.go
index d6275a6..d81deac 100644
--- a/syntax.go
+++ b/syntax.go
@@ -144,6 +144,10 @@ func (s *Syntax) Init() error {
 		return ErrRootAlias
 	}
 
+	if err := s.root.normalize(s.registry, &idSet{}); err != nil {
+		return err
+	}
+
 	for _, p := range s.registry.definitions {
 		p.init(s.registry)
 	}