diff --git a/src/app/container/calculator.cpp b/src/app/container/calculator.cpp
index 34e629328..6d04df791 100644
--- a/src/app/container/calculator.cpp
+++ b/src/app/container/calculator.cpp
@@ -110,6 +110,10 @@ qreal Calculator::EvalFormula(const QString &formula)
     result = Eval();
 
     QMap<int, QString> tokens = this->GetTokens();
+
+    // Remove "-" from tokens list if exist. If don't do that unary minus operation will broken.
+    RemoveAll(tokens, "-");
+
     if (tokens.isEmpty())
     {
         return result;
@@ -243,3 +247,16 @@ void Calculator::SetSepForTr(bool fromUser)
         SetDecSep('.');
     }
 }
+
+//---------------------------------------------------------------------------------------------------------------------
+void Calculator::RemoveAll(QMap<int, QString> &map, const QString &val)
+{
+    QList<int> listKeys = map.keys(val);
+    if (listKeys.size() > 0)
+    {
+        for (int i = 0; i < listKeys.size(); ++i)
+        {
+            map.remove(listKeys.at(i));
+        }
+    }
+}
diff --git a/src/app/container/calculator.h b/src/app/container/calculator.h
index 4431edf3c..c71cae22b 100644
--- a/src/app/container/calculator.h
+++ b/src/app/container/calculator.h
@@ -68,6 +68,7 @@ private:
     static qreal* AddVariable(const QString &a_szName, void *a_pUserData);
     void          SetSepForEval();
     void          SetSepForTr(bool fromUser);
+    void          RemoveAll(QMap<int, QString> &map, const QString &val);
 };
 
 #endif // CALCULATOR_H