diff --git a/include/fintamath/expressions/Expression.hpp b/include/fintamath/expressions/Expression.hpp
index 81e9270e5..d6e0aa6b1 100644
--- a/include/fintamath/expressions/Expression.hpp
+++ b/include/fintamath/expressions/Expression.hpp
@@ -43,7 +43,7 @@ class Expression : public IExpressionCRTP<Expression> {
 
   void setChildren(const ArgumentsPtrVector &childVect) override;
 
-  void setVariables(const std::vector<Variable> &vars, const ArgumentsPtrVector &vals) override;
+  void setVariables(const std::vector<std::pair<Variable, ArgumentPtr>> &varsToVals) override;
 
   void setVariable(const Variable &var, const Expression &val);
 
diff --git a/include/fintamath/expressions/IExpression.hpp b/include/fintamath/expressions/IExpression.hpp
index 70798d96d..c3ca7fc1a 100644
--- a/include/fintamath/expressions/IExpression.hpp
+++ b/include/fintamath/expressions/IExpression.hpp
@@ -19,7 +19,7 @@ class IExpression : public IArithmetic {
 
   std::vector<Variable> getVariables() const;
 
-  virtual void setVariables(const std::vector<Variable> &vars, const ArgumentsPtrVector &vals);
+  virtual void setVariables(const std::vector<std::pair<Variable, ArgumentPtr>> &varsToVals);
 
   std::unique_ptr<IMathObject> toMinimalObject() const final;
 
diff --git a/src/fintamath/expressions/Expression.cpp b/src/fintamath/expressions/Expression.cpp
index b02395349..ce0692ed0 100644
--- a/src/fintamath/expressions/Expression.cpp
+++ b/src/fintamath/expressions/Expression.cpp
@@ -517,13 +517,13 @@ void Expression::setChildren(const ArgumentsPtrVector &childVect) {
   child = childVect.front()->toMinimalObject();
 }
 
-void Expression::setVariables(const std::vector<Variable> &vars, const ArgumentsPtrVector &vals) {
-  IExpression::setVariables(vars, vals);
+void Expression::setVariables(const std::vector<std::pair<Variable, ArgumentPtr>> &varsToVals) {
+  IExpression::setVariables(varsToVals);
   simplifyChild(child);
 }
 
 void Expression::setVariable(const Variable &var, const Expression &val) {
-  setVariables({var}, ArgumentsPtrVector{val.getChildren().front()});
+  setVariables({{var, val.child}});
 }
 
 Expression operator+(const Variable &lhs, const Variable &rhs) {
diff --git a/src/fintamath/expressions/IExpression.cpp b/src/fintamath/expressions/IExpression.cpp
index 333c29621..45beaa9f4 100644
--- a/src/fintamath/expressions/IExpression.cpp
+++ b/src/fintamath/expressions/IExpression.cpp
@@ -32,25 +32,27 @@ std::vector<Variable> IExpression::getVariables() const {
   return vars;
 }
 
-void IExpression::setVariables(const std::vector<Variable> &vars, const ArgumentsPtrVector &vals) {
+void IExpression::setVariables(const std::vector<std::pair<Variable, ArgumentPtr>> &varsToVals) {
   auto children = getChildren();
 
   ArgumentsPtrVector newChildren;
 
   for (auto &child : children) {
     if (std::shared_ptr<IExpression> exprChild = cast<IExpression>(child->clone())) {
-      exprChild->setVariables(vars, vals);
+      exprChild->setVariables(varsToVals);
       newChildren.emplace_back(exprChild);
       continue;
     }
 
     bool isAdded = false;
 
-    for (size_t i = 0; i < vars.size(); i++) {
-      if (const auto varChild = cast<Variable>(child); varChild && *varChild == vars[i]) {
-        newChildren.push_back(vals[i]->clone());
-        isAdded = true;
-        break;
+    if (const auto varChild = cast<Variable>(child)) {
+      for (const auto &varsToVal : varsToVals) {
+        if (*varChild == varsToVal.first) {
+          newChildren.push_back(varsToVal.second);
+          isAdded = true;
+          break;
+        }
       }
     }
 
diff --git a/src/fintamath/expressions/functions/ExpressionFunctionSolve.cpp b/src/fintamath/expressions/functions/ExpressionFunctionSolve.cpp
index c923cee00..65a71e83e 100644
--- a/src/fintamath/expressions/functions/ExpressionFunctionSolve.cpp
+++ b/src/fintamath/expressions/functions/ExpressionFunctionSolve.cpp
@@ -189,13 +189,22 @@ ArgumentsPtrVector solveQuadraticEquation(const ArgumentsPtrVector &coeffAtPow)
   // TODO: remove this try/catch when complex numbers will be implemented
   try {
     Expression firstRootValue = firstRoot;
-    firstRootValue.setVariables({c, b, a}, coeffAtPow);
+    firstRootValue.setVariables({
+        {c, coeffAtPow[0]}, //
+        {b, coeffAtPow[1]}, //
+        {a, coeffAtPow[2]}, //
+    });
 
     Expression secondRootValue = secondRoot;
-    secondRootValue.setVariables({c, b, a}, coeffAtPow);
+    secondRootValue.setVariables({
+        {c, coeffAtPow[0]}, //
+        {b, coeffAtPow[1]}, //
+        {a, coeffAtPow[2]}, //
+    });
 
     return {firstRootValue.getChildren().front(), secondRootValue.getChildren().front()};
   }
+
   catch (const UndefinedException &) {
     return {};
   }