diff --git a/apps/solver/equation_store.cpp b/apps/solver/equation_store.cpp
index af295b151..093a10d68 100644
--- a/apps/solver/equation_store.cpp
+++ b/apps/solver/equation_store.cpp
@@ -107,7 +107,7 @@ EquationStore::Error EquationStore::exactSolve(Poincare::Context * context) {
     if (e.isUninitialized() || e.type() == ExpressionNode::Type::Undefined) {
       return Error::EquationUndefined;
     }
-    numberOfVariables = definedModelAtIndex(i)->standardForm(context).getVariables(*context, [](const char * symbol) { return true; }, (char *)m_variables, Equation::k_maxVariableSize);
+    numberOfVariables = e.getVariables(*context, [](const char * symbol) { return true; }, (char *)m_variables, Equation::k_maxVariableSize);
     if (numberOfVariables == -1) {
       return Error::TooManyVariables;
     }