diff --git a/poincare/src/prediction_interval.cpp b/poincare/src/prediction_interval.cpp
index 04298ff8a..fe93d73bb 100644
--- a/poincare/src/prediction_interval.cpp
+++ b/poincare/src/prediction_interval.cpp
@@ -22,7 +22,7 @@ Expression::Type PredictionInterval::type() const {
 
 Expression * PredictionInterval::cloneWithDifferentOperands(Expression** newOperands,
         int numberOfOperands, bool cloneOperands) const {
-  assert(numberOfOperands == 1);
+  assert(numberOfOperands == 2);
   assert(newOperands != nullptr);
   PredictionInterval * pi = new PredictionInterval();
   pi->setArgument(newOperands, numberOfOperands, cloneOperands);