diff --git a/VAR.ExpressionEvaluator.Tests/ParserTests.cs b/VAR.ExpressionEvaluator.Tests/ParserTests.cs
index 31d59af..b8402da 100644
--- a/VAR.ExpressionEvaluator.Tests/ParserTests.cs
+++ b/VAR.ExpressionEvaluator.Tests/ParserTests.cs
@@ -241,6 +241,19 @@ namespace VAR.ExpressionEvaluator.Tests
             Assert.Equal(4m, result);
         }
 
+        [Fact]
+        public void Functions__ZeroParameters()
+        {
+            EvaluationContext evaluationContex = new EvaluationContext();
+            evaluationContex.SetFunction("constant", (parameters) =>
+            {
+                return 9m;
+            });
+            string expression = "constant()";
+            object result = Parser.EvaluateString(expression, evaluationContex);
+            Assert.Equal(9m, result);
+        }
+
         #endregion Functions
 
         #region Strings
@@ -252,6 +265,14 @@ namespace VAR.ExpressionEvaluator.Tests
             object result = Parser.EvaluateString(expression);
             Assert.Equal("Hello World", result);
         }
+        
+        [Fact]
+        public void Strings__Contatenate_Hello_World_SimpleQuotes()
+        {
+            string expression = "'Hello' + ' ' +'World'";
+            object result = Parser.EvaluateString(expression);
+            Assert.Equal("Hello World", result);
+        }
 
         [Fact]
         public void Strings__Contatenate_Hello_World_WithVariables()
diff --git a/VAR.ExpressionEvaluator/Parser.cs b/VAR.ExpressionEvaluator/Parser.cs
index c6744e5..be23c76 100644
--- a/VAR.ExpressionEvaluator/Parser.cs
+++ b/VAR.ExpressionEvaluator/Parser.cs
@@ -239,15 +239,18 @@ namespace VAR.ExpressionEvaluator
                 {
                     _tokenizer.NextToken();
                     var parameters = new List<IExpressionNode>();
-                    while (true)
+                    if (_tokenizer.Token != Token.ParenthesisEnd)
                     {
-                        parameters.Add(ParseBooleanOp());
-                        if (_tokenizer.Token == Token.Comma)
+                        while (true)
                         {
-                            _tokenizer.NextToken();
-                            continue;
+                            parameters.Add(ParseBooleanOp());
+                            if (_tokenizer.Token == Token.Comma)
+                            {
+                                _tokenizer.NextToken();
+                                continue;
+                            }
+                            break;
                         }
-                        break;
                     }
                     if (_tokenizer.Token != Token.ParenthesisEnd)
                     {