diff --git a/MathParser.cs b/MathParser.cs
index 175ac37..01e11a7 100644
--- a/MathParser.cs
+++ b/MathParser.cs
@@ -305,7 +305,7 @@ private string LexicalAnalysisInfixNotation(string expression, ref int pos)
             if (supportedOperators.ContainsKey(token.ToString()))
             {
                 // Determine it is unary or binary operator
-                bool isUnary = pos == 0 || expression[pos - 1] == '(';
+                bool isUnary = pos == 0 || "+-*/^(".Contains(expression[pos - 1].ToString());
                 pos++;
 
                 switch (token.ToString())
@@ -739,4 +739,4 @@ private int NumberOfArguments(string token)
 
         #endregion
     }
-}
\ No newline at end of file
+}