diff --git a/apps/solver/base.de.i18n b/apps/solver/base.de.i18n
index ab32b9dce..843c7dea8 100644
--- a/apps/solver/base.de.i18n
+++ b/apps/solver/base.de.i18n
@@ -4,6 +4,7 @@ AddEquation = "Ajouter une équation"
 Resolve = "Résoudre l'équation"
 RequireEquation = "L'entrée doit être une équation"
 UseEquationModel = "Utiliser le modèle d'équation"
+UndefinedEquation = "Une equation est indéfinie"
 TooManyVariables = "Le système a trop d'inconnus"
 NonLinearSystem = "Le système n'est pas linéaire"
 Solution = "Solution"
diff --git a/apps/solver/base.en.i18n b/apps/solver/base.en.i18n
index ab32b9dce..843c7dea8 100644
--- a/apps/solver/base.en.i18n
+++ b/apps/solver/base.en.i18n
@@ -4,6 +4,7 @@ AddEquation = "Ajouter une équation"
 Resolve = "Résoudre l'équation"
 RequireEquation = "L'entrée doit être une équation"
 UseEquationModel = "Utiliser le modèle d'équation"
+UndefinedEquation = "Une equation est indéfinie"
 TooManyVariables = "Le système a trop d'inconnus"
 NonLinearSystem = "Le système n'est pas linéaire"
 Solution = "Solution"
diff --git a/apps/solver/base.es.i18n b/apps/solver/base.es.i18n
index ab32b9dce..843c7dea8 100644
--- a/apps/solver/base.es.i18n
+++ b/apps/solver/base.es.i18n
@@ -4,6 +4,7 @@ AddEquation = "Ajouter une équation"
 Resolve = "Résoudre l'équation"
 RequireEquation = "L'entrée doit être une équation"
 UseEquationModel = "Utiliser le modèle d'équation"
+UndefinedEquation = "Une equation est indéfinie"
 TooManyVariables = "Le système a trop d'inconnus"
 NonLinearSystem = "Le système n'est pas linéaire"
 Solution = "Solution"
diff --git a/apps/solver/base.fr.i18n b/apps/solver/base.fr.i18n
index ab32b9dce..843c7dea8 100644
--- a/apps/solver/base.fr.i18n
+++ b/apps/solver/base.fr.i18n
@@ -4,6 +4,7 @@ AddEquation = "Ajouter une équation"
 Resolve = "Résoudre l'équation"
 RequireEquation = "L'entrée doit être une équation"
 UseEquationModel = "Utiliser le modèle d'équation"
+UndefinedEquation = "Une equation est indéfinie"
 TooManyVariables = "Le système a trop d'inconnus"
 NonLinearSystem = "Le système n'est pas linéaire"
 Solution = "Solution"
diff --git a/apps/solver/base.pt.i18n b/apps/solver/base.pt.i18n
index ab32b9dce..843c7dea8 100644
--- a/apps/solver/base.pt.i18n
+++ b/apps/solver/base.pt.i18n
@@ -4,6 +4,7 @@ AddEquation = "Ajouter une équation"
 Resolve = "Résoudre l'équation"
 RequireEquation = "L'entrée doit être une équation"
 UseEquationModel = "Utiliser le modèle d'équation"
+UndefinedEquation = "Une equation est indéfinie"
 TooManyVariables = "Le système a trop d'inconnus"
 NonLinearSystem = "Le système n'est pas linéaire"
 Solution = "Solution"
diff --git a/apps/solver/equation.cpp b/apps/solver/equation.cpp
index 4468d24e2..9f00539ac 100644
--- a/apps/solver/equation.cpp
+++ b/apps/solver/equation.cpp
@@ -40,10 +40,12 @@ Expression * Equation::standardForm(Context * context) const {
     Expression * e = expression(context);
     if (e->type() == Expression::Type::Equal) {
       m_standardForm = static_cast<const Equal *>(e)->standardEquation(*context);
-    } else {
+    } else if (e->type() == Expression::Type::Rational && static_cast<Rational *>(e)->isOne()) {
       // The equality was reduced which means the equality was always true.
-      assert(e->type() == Expression::Type::Rational && static_cast<Rational *>(e)->isOne());
       m_standardForm = new Rational(0);
+    } else {
+      // The equality has an undefined operand
+      assert(e->type() == Expression::Type::Undefined);
     }
   }
   return m_standardForm;
diff --git a/apps/solver/equation_store.cpp b/apps/solver/equation_store.cpp
index 4733ca683..60298dc40 100644
--- a/apps/solver/equation_store.cpp
+++ b/apps/solver/equation_store.cpp
@@ -72,6 +72,7 @@ bool EquationStore::haveMoreApproximationSolutions(Context * context) {
 
 void EquationStore::approximateSolve(Poincare::Context * context) {
   assert(m_variables[0] != 0 && m_variables[1] == 0);
+  assert(m_type == Type::Monovariable);
   m_numberOfSolutions = 0;
   double start = m_intervalApproximateSolutions[0];
   double step = (m_intervalApproximateSolutions[1]-m_intervalApproximateSolutions[0])*k_precision;
@@ -93,6 +94,9 @@ EquationStore::Error EquationStore::exactSolve(Poincare::Context * context) {
   m_variables[0] = 0;
   int numberOfVariables = 0;
   for (int i = 0; i < numberOfDefinedModels(); i++) {
+    if (definedModelAtIndex(i)->standardForm(context) == nullptr) {
+      return Error::EquationUndefined;
+    }
     numberOfVariables = definedModelAtIndex(i)->standardForm(context)->getVariables(m_variables);
     if (numberOfVariables < 0) {
       return Error::TooManyVariables;
diff --git a/apps/solver/equation_store.h b/apps/solver/equation_store.h
index 03ccdf562..f761c72ab 100644
--- a/apps/solver/equation_store.h
+++ b/apps/solver/equation_store.h
@@ -16,9 +16,10 @@ public:
   };
   enum class Error : int16_t {
     NoError = 0,
-    TooManyVariables = -1,
-    NonLinearSystem = -2,
-    RequireApproximateSolution = -3
+    EquationUndefined = -1,
+    TooManyVariables = -2,
+    NonLinearSystem = -3,
+    RequireApproximateSolution = -4
   };
   EquationStore();
   ~EquationStore();
diff --git a/apps/solver/list_controller.cpp b/apps/solver/list_controller.cpp
index da8f148df..19f7b0022 100644
--- a/apps/solver/list_controller.cpp
+++ b/apps/solver/list_controller.cpp
@@ -147,6 +147,9 @@ void ListController::resolveEquations() {
   }
   EquationStore::Error e = m_equationStore->exactSolve(static_cast<App *>(app())->localContext());
   switch (e) {
+    case EquationStore::Error::EquationUndefined:
+      app()->displayWarning(I18n::Message::UndefinedEquation);
+      return;
     case EquationStore::Error::TooManyVariables:
       app()->displayWarning(I18n::Message::TooManyVariables);
       return;