diff --git a/poincare/include/poincare/expression.h b/poincare/include/poincare/expression.h
index 035bee916..c25ddd2d4 100644
--- a/poincare/include/poincare/expression.h
+++ b/poincare/include/poincare/expression.h
@@ -13,6 +13,7 @@ namespace Poincare {
 class Context;
 
 class Expression : public TreeByReference {
+  friend class AbsoluteValue;
   friend class CosineNode;
   friend class SineNode;
   friend class ExpressionNode;
diff --git a/poincare/src/absolute_value.cpp b/poincare/src/absolute_value.cpp
index a13fb6438..21fb0166c 100644
--- a/poincare/src/absolute_value.cpp
+++ b/poincare/src/absolute_value.cpp
@@ -43,19 +43,22 @@ Expression AbsoluteValue::shallowReduce(Context & context, Preferences::AngleUni
   if (e.isUndefinedOrAllocationFailure()) {
     return e;
   }
-  Expression op = childAtIndex(0);
+  Expression c = childAtIndex(0);
 #if MATRIX_EXACT_REDUCING
 #if 0
-  if (op->type() == Type::Matrix) {
+  if (c->type() == Type::Matrix) {
     return SimplificationHelper::Map(this, context, angleUnit);
   }
 #endif
 #endif
-  if (op.sign() == ExpressionNode::Sign::Positive) {
-    return op;
+  if (c.sign() == ExpressionNode::Sign::Positive) {
+    replaceWithInPlace(c);
+    return c;
   }
-  if (op.sign() == ExpressionNode::Sign::Negative) {
-    return op.setSign(ExpressionNode::Sign::Positive, context, angleUnit);
+  if (c.sign() == ExpressionNode::Sign::Negative) {
+    Expression result = c.setSign(ExpressionNode::Sign::Positive, context, angleUnit);
+    replaceWithInPlace(result);
+    return result;
   }
   return *this;
 }