diff --git a/cgmes/cgmes-conversion/src/main/java/com/powsybl/cgmes/conversion/elements/transformers/InterpretedT3xModel.java b/cgmes/cgmes-conversion/src/main/java/com/powsybl/cgmes/conversion/elements/transformers/InterpretedT3xModel.java
index 3a33af8e5ad..d95a3e6cc50 100644
--- a/cgmes/cgmes-conversion/src/main/java/com/powsybl/cgmes/conversion/elements/transformers/InterpretedT3xModel.java
+++ b/cgmes/cgmes-conversion/src/main/java/com/powsybl/cgmes/conversion/elements/transformers/InterpretedT3xModel.java
@@ -66,7 +66,7 @@ static class InterpretedWinding {
         final TapChangerConversion.InterpretedEnd end1;
         final InterpretedEnd2 end2;
         final boolean structuralRatioAtEnd2;
-        final double ratedS;
+        final Double ratedS;
 
         /**
          * Maps Cgmes ratioTapChangers, phaseTapChangers, shuntAdmittances and