diff --git a/ASN1-Model/ASN1AdaptiveTypeObject.class.st b/ASN1-Model/ASN1AdaptiveTypeObject.class.st
index ef0f8da..3914c99 100644
--- a/ASN1-Model/ASN1AdaptiveTypeObject.class.st
+++ b/ASN1-Model/ASN1AdaptiveTypeObject.class.st
@@ -3,7 +3,8 @@ Class {
 	#superclass : 'ASN1AdaptiveTypeValue',
 	#instVars : [
 		'map',
-		'selfExpanding'
+		'selfExpanding',
+		'addedByDefault'
 	],
 	#category : 'ASN1-Model',
 	#package : 'ASN1-Model'
@@ -19,6 +20,12 @@ ASN1AdaptiveTypeObject class >> typedCollection [
 	^ ASN1TypedCollectionType type: self
 ]
 
+{ #category : 'accessing' }
+ASN1AdaptiveTypeObject >> addedByDefault: aKey [ 
+	addedByDefault ifNil: [ addedByDefault := OrderedCollection new ].
+	addedByDefault add: aKey 
+]
+
 { #category : 'accessing' }
 ASN1AdaptiveTypeObject >> at: aKey [
 	^ self 
@@ -282,3 +289,9 @@ ASN1AdaptiveTypeObject >> size [
 ASN1AdaptiveTypeObject >> soleValue [
 	^ map values first
 ]
+
+{ #category : 'as yet unclassified' }
+ASN1AdaptiveTypeObject >> wasAddedByDefault: aKey [ 
+	addedByDefault ifNil: [ ^ false ].
+	^ addedByDefault includes: aKey
+]
diff --git a/ASN1-Tool/ASN1ReadVisitor.class.st b/ASN1-Tool/ASN1ReadVisitor.class.st
index 3851778..af0f10d 100644
--- a/ASN1-Tool/ASN1ReadVisitor.class.st
+++ b/ASN1-Tool/ASN1ReadVisitor.class.st
@@ -166,7 +166,8 @@ ASN1ReadVisitor >> visitCollection: aCollection [
 								"write the default value in the result"
 								element value defaultValue isAsn1 
 									ifTrue: [ value baseValueAt: element key put: element value defaultValue ]
-									ifFalse: [ value at: element key put: element value defaultValue ] ].
+									ifFalse: [ value at: element key put: element value defaultValue ].
+								value addedByDefault: element key ].
 							elementStream next  ]						
 						ifFalse: [ isExtended ifTrue: [ 
 							(aCollection hasElementWithTag: content tag) ifFalse: [
diff --git a/ASN1-Tool/ASN1WriteVisitor.class.st b/ASN1-Tool/ASN1WriteVisitor.class.st
index b4be9fd..90bf356 100644
--- a/ASN1-Tool/ASN1WriteVisitor.class.st
+++ b/ASN1-Tool/ASN1WriteVisitor.class.st
@@ -2,13 +2,20 @@ Class {
 	#name : 'ASN1WriteVisitor',
 	#superclass : 'ASN1ModelVisitor',
 	#instVars : [
-		'currentValue'
+		'currentValue',
+		'skipAddedDefaults'
 	],
 	#category : 'ASN1-Tool-Visitor',
 	#package : 'ASN1-Tool',
 	#tag : 'Visitor'
 }
 
+{ #category : 'initialization' }
+ASN1WriteVisitor >> initialize [
+	super initialize.
+	skipAddedDefaults := true
+]
+
 { #category : 'exceptions' }
 ASN1WriteVisitor >> mandatoryElementNotFound [
 	ASN1MandatoryElementNotFound signal
@@ -23,6 +30,11 @@ ASN1WriteVisitor >> push: anObject during: aBlock [
 	^aBlock ensure: [ currentValue := formerValue ]
 ]
 
+{ #category : 'accessing' }
+ASN1WriteVisitor >> skipAddedDefaults [ 
+	skipAddedDefaults := true
+]
+
 { #category : 'visiting' }
 ASN1WriteVisitor >> visit: aType [
 	(aType isNil ifTrue: [ Error signal: 'type cannot be nil' ]).
@@ -101,18 +113,19 @@ ASN1WriteVisitor >> visitSequenceType: aSequence [
 	object := currentValue "basicValue".
 	aSequence elements associations do:  [ :each |
 		(each value class = ASN1Extension) ifFalse: [   
-			(object includesKey: each key) 
-				ifTrue: [ 
-					self 
-						push: (object privAt: each key)
-						during: [ encoded elements add: (self visit: (aSequence elementAt: each key)) ]]
-				ifFalse: [
-					each value isOptional
-						ifTrue: [ each value hasDefaultValue ifTrue: [ 
-							self 
-								push: each value defaultValue 
-								during: [ encoded elements add: (self visit: (aSequence elementAt: each key) value) ] ] ]
-						ifFalse: [ self mandatoryElementNotFound ] ] ] ].
+			(skipAddedDefaults and: [ object wasAddedByDefault: each key ]) ifFalse:  [  
+				(object includesKey: each key)
+					ifTrue: [ 
+						self 
+							push: (object privAt: each key)
+							during: [ encoded elements add: (self visit: (aSequence elementAt: each key)) ]]
+					ifFalse: [
+						each value isOptional
+							ifTrue: [ each value hasDefaultValue ifTrue: [ 
+								self 
+									push: each value defaultValue 
+									during: [ encoded elements add: (self visit: (aSequence elementAt: each key) defaultValue type ) ] ] ]
+							ifFalse: [ self mandatoryElementNotFound ] ] ] ] ].
 	^ encoded
 ]