diff --git a/contracts/evoting/types/ballots.go b/contracts/evoting/types/ballots.go
index e8f8eb14..770af369 100644
--- a/contracts/evoting/types/ballots.go
+++ b/contracts/evoting/types/ballots.go
@@ -334,7 +334,9 @@ func (s *Subject) MaxEncodedSize() int {
 	//TODO : optimise by computing max size according to number of choices and maxN
 	for _, rank := range s.Ranks {
 		size += len(rank.GetID())
-		size += len(rank.ID)
+		// the ID arrives Base64-encoded, but rank.ID is decoded
+		// we need the size of the Base64-encoded string
+		size += len(base64.StdEncoding.EncodeToString([]byte(rank.ID)))
 
 		// ':' separators ('id:id:choice')
 		size += 2
@@ -345,7 +347,9 @@ func (s *Subject) MaxEncodedSize() int {
 
 	for _, selection := range s.Selects {
 		size += len(selection.GetID())
-		size += len(selection.ID)
+		// the ID arrives Base64-encoded, but selection.ID is decoded
+		// we need the size of the Base64-encoded string
+		size += len(base64.StdEncoding.EncodeToString([]byte(selection.ID)))
 
 		// ':' separators ('id:id:choice')
 		size += 2
@@ -356,7 +360,9 @@ func (s *Subject) MaxEncodedSize() int {
 
 	for _, text := range s.Texts {
 		size += len(text.GetID())
-		size += len(text.ID)
+		// the ID arrives Base64-encoded, but text.ID is decoded
+		// we need the size of the Base64-encoded string
+		size += len(base64.StdEncoding.EncodeToString([]byte(text.ID)))
 
 		// ':' separators ('id:id:choice')
 		size += 2
diff --git a/contracts/evoting/types/ballots_test.go b/contracts/evoting/types/ballots_test.go
index 9b292f73..f47bddfd 100644
--- a/contracts/evoting/types/ballots_test.go
+++ b/contracts/evoting/types/ballots_test.go
@@ -314,13 +314,13 @@ func TestSubject_MaxEncodedSize(t *testing.T) {
 		}},
 
 		Selects: []Select{{
-			ID:      encodedQuestionID(1),
+			ID:      decodedQuestionID(1),
 			Title:   Title{En: "", Fr: "", De: "", URL: ""},
 			MaxN:    3,
 			MinN:    0,
 			Choices: make([]Choice, 3),
 		}, {
-			ID:      encodedQuestionID(2),
+			ID:      decodedQuestionID(2),
 			Title:   Title{En: "", Fr: "", De: "", URL: ""},
 			MaxN:    5,
 			MinN:    0,
@@ -328,7 +328,7 @@ func TestSubject_MaxEncodedSize(t *testing.T) {
 		}},
 
 		Ranks: []Rank{{
-			ID:      encodedQuestionID(3),
+			ID:      decodedQuestionID(3),
 			Title:   Title{En: "", Fr: "", De: "", URL: ""},
 			MaxN:    4,
 			MinN:    0,
@@ -336,7 +336,7 @@ func TestSubject_MaxEncodedSize(t *testing.T) {
 		}},
 
 		Texts: []Text{{
-			ID:        encodedQuestionID(4),
+			ID:        decodedQuestionID(4),
 			Title:     Title{En: "", Fr: "", De: "", URL: ""},
 			MaxN:      2,
 			MinN:      0,
@@ -344,7 +344,7 @@ func TestSubject_MaxEncodedSize(t *testing.T) {
 			Regex:     "",
 			Choices:   make([]Choice, 2),
 		}, {
-			ID:        encodedQuestionID(5),
+			ID:        decodedQuestionID(5),
 			Title:     Title{En: "", Fr: "", De: "", URL: ""},
 			MaxN:      1,
 			MinN:      0,