diff --git a/variable/registry.go b/variable/registry.go
index d68910a..1b23249 100644
--- a/variable/registry.go
+++ b/variable/registry.go
@@ -59,7 +59,7 @@ var DefaultRegistry = Registry{
 
 // Register registers a new variable.
 func Register[T any, Option RegisterOption](
-	spec TypedSpec[T],
+	spec *TypedSpec[T],
 	options ...Option,
 ) *OfType[T] {
 	opts := registerOptions{
diff --git a/variable/spec.go b/variable/spec.go
index 9f1dc9d..001370c 100644
--- a/variable/spec.go
+++ b/variable/spec.go
@@ -68,45 +68,45 @@ type TypedSpec[T any] struct {
 }
 
 // Name returns the name of the variable.
-func (s TypedSpec[T]) Name() string {
+func (s *TypedSpec[T]) Name() string {
 	return s.name
 }
 
 // Description returns a human-readable description of the variable.
-func (s TypedSpec[T]) Description() string {
+func (s *TypedSpec[T]) Description() string {
 	return s.desc
 }
 
 // Schema returns the schema that applies to the variable's value.
-func (s TypedSpec[T]) Schema() Schema {
+func (s *TypedSpec[T]) Schema() Schema {
 	return s.schema
 }
 
 // Default returns the string representation of the default value.
-func (s TypedSpec[T]) Default() (Literal, bool) {
+func (s *TypedSpec[T]) Default() (Literal, bool) {
 	return maybe.Map(s.def, valueOf[T].Canonical).Get()
 }
 
 // IsRequired returns true if the application MUST have a value for this
 // variable (even if it is fulfilled by a default value).
-func (s TypedSpec[T]) IsRequired() bool {
+func (s *TypedSpec[T]) IsRequired() bool {
 	return s.required
 }
 
 // IsSensitive returns true if the variable's value contains sensitive
 // information.
-func (s TypedSpec[T]) IsSensitive() bool {
+func (s *TypedSpec[T]) IsSensitive() bool {
 	return s.sensitive
 }
 
 // IsDeprecated returns true if the variable is deprecated.
-func (s TypedSpec[T]) IsDeprecated() bool {
+func (s *TypedSpec[T]) IsDeprecated() bool {
 	return s.deprecated
 }
 
 // Constraints returns a list of additional constraints on the variable's
 // value.
-func (s TypedSpec[T]) Constraints() []Constraint {
+func (s *TypedSpec[T]) Constraints() []Constraint {
 	constraints := make([]Constraint, len(s.constraints))
 	for i, c := range s.constraints {
 		constraints[i] = c
@@ -115,18 +115,18 @@ func (s TypedSpec[T]) Constraints() []Constraint {
 }
 
 // Examples returns a list of examples of valid values.
-func (s TypedSpec[T]) Examples() []Example {
+func (s *TypedSpec[T]) Examples() []Example {
 	return s.examples
 }
 
 // Documentation returns a list of chunks of documentation text.
-func (s TypedSpec[T]) Documentation() []Documentation {
+func (s *TypedSpec[T]) Documentation() []Documentation {
 	return s.docs
 }
 
 // CheckConstraints returns an error if v does not satisfy any one of the
 // specification's constraints.
-func (s TypedSpec[T]) CheckConstraints(v T) ConstraintError {
+func (s *TypedSpec[T]) CheckConstraints(v T) ConstraintError {
 	for _, c := range s.constraints {
 		if err := c.Check(v); err != nil {
 			return err
@@ -140,7 +140,7 @@ func (s TypedSpec[T]) CheckConstraints(v T) ConstraintError {
 //
 // It returns an error if v does not meet the specification's constraints or
 // marshaling fails at the schema level.
-func (s TypedSpec[T]) Marshal(v T) (Literal, error) {
+func (s *TypedSpec[T]) Marshal(v T) (Literal, error) {
 	if err := s.CheckConstraints(v); err != nil {
 		return Literal{}, err
 	}
@@ -152,7 +152,7 @@ func (s TypedSpec[T]) Marshal(v T) (Literal, error) {
 //
 // It returns an error if v does not meet the specification's constraints or
 // unmarshaling fails at the schema level.
-func (s TypedSpec[T]) Unmarshal(v Literal) (T, Literal, error) {
+func (s *TypedSpec[T]) Unmarshal(v Literal) (T, Literal, error) {
 	n, err := s.schema.Unmarshal(v)
 	if err != nil {
 		return n, Literal{}, err
diff --git a/variable/specbuilder.go b/variable/specbuilder.go
index f61a410..ff68e55 100644
--- a/variable/specbuilder.go
+++ b/variable/specbuilder.go
@@ -109,14 +109,14 @@ func (b *TypedSpecBuilder[T]) Documentation() DocumentationBuilder {
 }
 
 // Done builds the specification and registers the variable.
-func (b *TypedSpecBuilder[T]) Done(schema TypedSchema[T]) TypedSpec[T] {
+func (b *TypedSpecBuilder[T]) Done(schema TypedSchema[T]) *TypedSpec[T] {
 	b.spec.schema = schema
 
 	if err := b.finalize(); err != nil {
 		panic(err.Error())
 	}
 
-	return b.spec
+	return &b.spec
 }
 
 func (b *TypedSpecBuilder[T]) finalize() error {
diff --git a/variable/variable.go b/variable/variable.go
index 8e829df..6819a64 100644
--- a/variable/variable.go
+++ b/variable/variable.go
@@ -25,7 +25,7 @@ type Any interface {
 
 // OfType is an environment variable depicted by type T.
 type OfType[T any] struct {
-	spec TypedSpec[T]
+	spec *TypedSpec[T]
 	env  Environment
 
 	once     sync.Once