diff --git a/engine/calldesc.go b/engine/calldesc.go
index bf61cc4a2..755a0a61f 100644
--- a/engine/calldesc.go
+++ b/engine/calldesc.go
@@ -424,7 +424,8 @@ and will decrease it by 10% for nine times. So if the user has little credit it
 If the user has no credit then it will return 0.
 If the user has postpayed plan it returns -1.
 */
-func (cd *CallDescriptor) GetMaxSessionDuration() (time.Duration, error) {
+func (origCd *CallDescriptor) GetMaxSessionDuration() (time.Duration, error) {
+	cd := origCd.Clone()
 	if cd.CallDuration == 0 {
 		cd.CallDuration = cd.TimeEnd.Sub(cd.TimeStart)
 	}
@@ -614,3 +615,22 @@ func (cd *CallDescriptor) CreateCallCost() *CallCost {
 		Destination: cd.Destination,
 	}
 }
+
+func (cd *CallDescriptor) Clone() *CallDescriptor {
+	return &CallDescriptor{
+		Direction:       cd.Direction,
+		TOR:             cd.TOR,
+		Tenant:          cd.Tenant,
+		Subject:         cd.Subject,
+		Account:         cd.Account,
+		Destination:     cd.Destination,
+		TimeStart:       cd.TimeStart,
+		TimeEnd:         cd.TimeEnd,
+		LoopIndex:       cd.LoopIndex,
+		CallDuration:    cd.CallDuration,
+		Amount:          cd.Amount,
+		FallbackSubject: cd.FallbackSubject,
+		RatingInfos:     cd.RatingInfos,
+		Increments:      cd.Increments,
+	}
+}
diff --git a/engine/calldesc_test.go b/engine/calldesc_test.go
index c5424d058..1e6ceb7db 100644
--- a/engine/calldesc_test.go
+++ b/engine/calldesc_test.go
@@ -20,6 +20,7 @@ package engine
 
 import (
 	"log"
+	"reflect"
 	"testing"
 	"time"
 
@@ -335,6 +336,23 @@ func TestMaxSessionTimeNoCredit(t *testing.T) {
 	}
 }
 
+func TestMaxSessionModifiesCallDesc(t *testing.T) {
+	cd := &CallDescriptor{
+		TimeStart:   time.Date(2013, 10, 21, 18, 34, 0, 0, time.UTC),
+		TimeEnd:     time.Date(2013, 10, 21, 18, 35, 0, 0, time.UTC),
+		Direction:   "*out",
+		TOR:         "0",
+		Tenant:      "vdf",
+		Subject:     "broker",
+		Destination: "0723",
+		Amount:      5400}
+	initial := cd.Clone()
+	cd.GetMaxSessionDuration()
+	if !reflect.DeepEqual(cd, initial) {
+		t.Errorf("GetMaxSessionDuration is changing the call descriptor %+v != %+v", cd, initial)
+	}
+}
+
 /*********************************** BENCHMARKS ***************************************/
 func BenchmarkStorageGetting(b *testing.B) {
 	b.StopTimer()