diff --git a/src/sly/parser/parser/Parser.cs b/src/sly/parser/parser/Parser.cs
index b133b61b..30c710bd 100644
--- a/src/sly/parser/parser/Parser.cs
+++ b/src/sly/parser/parser/Parser.cs
@@ -44,7 +44,12 @@ public virtual BuildResult<ParserConfiguration<IN, OUT>> BuildExpressionParser(
             var expressionGenerator = new ExpressionRulesGenerator<IN, OUT>(I18n);
             exprResult = expressionGenerator.BuildExpressionRules(Configuration, Instance.GetType(), exprResult);
             Configuration = exprResult.Result;
-            SyntaxParser.Init(exprResult.Result, startingRule);
+            if (exprResult.IsOk)
+            {
+                // #540 : recompute starting tokens taking account of expression rules 
+                SyntaxParser.Init(exprResult.Result, startingRule);
+            }
+
             if (startingRule != null)
             {
                 Configuration.StartingRule = startingRule;
diff --git a/src/sly/parser/parser/llparser/bnf/RecursiveDescentSyntaxParser.cs b/src/sly/parser/parser/llparser/bnf/RecursiveDescentSyntaxParser.cs
index 951b821c..54ab25d4 100644
--- a/src/sly/parser/parser/llparser/bnf/RecursiveDescentSyntaxParser.cs
+++ b/src/sly/parser/parser/llparser/bnf/RecursiveDescentSyntaxParser.cs
@@ -247,6 +247,11 @@ private SyntaxParseResult<IN, OUT> NoMatchingRuleError(IList<Token<IN>> tokens,
         public virtual void Init(ParserConfiguration<IN, OUT> configuration, string root)
         {
             if (root != null) StartingNonTerminal = root;
+            // #540 : reset all leading tokens and recompute with the new configuration (expression rules)
+            foreach (var nonTerminal in configuration.NonTerminals.Values)
+            {
+                nonTerminal?.Rules?.ForEach(x => x?.PossibleLeadingTokens?.Clear());
+            }
             InitializeStartingTokens(configuration, StartingNonTerminal);
         }
 
diff --git a/tests/ParserTests/Issue540/Issue540Parser.cs b/tests/ParserTests/Issue540/Issue540Parser.cs
new file mode 100644
index 00000000..ed6603bc
--- /dev/null
+++ b/tests/ParserTests/Issue540/Issue540Parser.cs
@@ -0,0 +1,254 @@
+
+using sly.parser.generator;
+using sly.parser.parser;
+using System.Collections.Generic;
+using sly.lexer;
+
+
+namespace ParserTests.Issue540
+{
+    public class Issue540Parser
+    {
+
+        [Production($"NtSection: NtStatement*")]
+        public object NTSection(List<object> a) => null;
+
+        [Production(
+            $"NtStatement: [NtSCExpr | NtLoop | NtCond | NtFunction | NtBlock | NtReturnStatement | NtLoopControlStatement]")]
+        public object NtStatement(object subStatement) => null;
+
+        [Production($"NtSCExpr: NtExpression Semicolon [d]")]
+
+        public object NtScExpr(object expression) => null;
+
+        [Production($"NtReturnStatement: Return [d] NtSCExpr")]
+        public object NtReturnStatement(object expr) => null;
+
+        [Production($"NtLoopControlStatement: [Break | Continue] NtNestedValueInLoopControl?")]
+        public object NtLoopControlStatement(Issue540Token op, ValueOption<object> nestedVal) => null;
+
+        [Production($"NtNestedValueInLoopControl: Identifier")]
+        public object NtNestedValueInLoopControl(Token<Issue540Token> val) => null;
+
+        [Production($"NtLoop: NtForLoopHeader NtLoopLabel? NtStatement NtElse?")]
+        [Production($"NtLoop: NtWhileLoopHeader NtLoopLabel? NtStatement NtElse?")]
+        public object NtLoop(object loopHeader, ValueOption<object> label, object statementExpr,
+            ValueOption<object> slseExpr) => null;
+
+        [Production($"NtLoopLabel: As [d] Identifier")]
+        public object NtLoopLabel(Token<Issue540Token> ident) => null;
+
+        [Production(
+            $"NtForLoopHeader: For [d] OpenParen [d] NtExpression Semicolon [d] NtExpression Semicolon [d] NtExpression CloseParen [d]")]
+        public object NtForLoopHeader(object init, object condition, object step) => null;
+
+        [Production($"NtWhileLoopHeader: While [d] OpenParen [d] NtExpression CloseParen [d]")]
+        public object NtWhileLoopHeader(object condition) => null;
+
+        [Production($"NtCond: [NtSwitch | NtIf]")]
+        public object NtCond(object _) => null;
+
+        [Production($"NtIf: If [d] OpenParen [d] NtExpression CloseParen [d] NtStatement NtElse?")]
+        public object NtIf(object a, object b, ValueOption<object> c) => null;
+
+        [Production($"NtElse: Else [d] NtStatement")]
+        public object NtElse(object _) => null;
+
+        [Production(
+            $"NtSwitch: Switch [d] OpenParen [d] NtExpression CloseParen [d] OpenCurly [d] NtSwitchBody* CloseCurly [d]")]
+        public object NtSwitch(object a, List<object> b) => null;
+
+        [Production($"NtSwitchBody: NtExpression Colon [d] NtStatement")]
+        public object NtSwitchBody(object a, object b) => null;
+
+        [Production($"NtFunction: NtType Identifier OpenParen [d] NtTypeAndIdentifierCSV? CloseParen [d] NtStatement")]
+        public object NtFunction(object a, Token<Issue540Token> b, ValueOption<object> c, object d) =>
+            null;
+
+        [Production($"NtTypeAndIdentifierCSV: NtTypeAndIdentifierCSVElement (Comma [d] NtTypeAndIdentifierCSV)*")]
+        public object NtTypeAndIdentifierCsv(object a, List<Group<Issue540Token, object>> b) => null;
+
+        [Production($"NtTypeAndIdentifierCSVElement: NtFunctionArgDeclModifiersCombined? NtType Identifier")]
+        public object NtTypeAndIdentifierCsvElement(ValueOption<object> a, object b, Token<Issue540Token> c) =>
+            null;
+
+        [Production($"NtBlock: OpenCurly [d] NtSection CloseCurly [d]")]
+        public object NtBlock(object a) => null;
+
+        [Production($"NtExpression: NtAliasExpr")]
+        public object NtExpression(object pass) => pass;
+
+        [Production($"NtAliasExpr: [NtAliasExpr1 | NtAliasExpr2 | NtAliasExpr3 | NtDeclarationExpr]")]
+        public object NtAliasExpr(object a) => null;
+
+        [Production($"NtAliasExpr1: Identifier As [d] Identifier")]
+        public object NtAliasExpr1(Token<Issue540Token> a, Token<Issue540Token> b) => null;
+
+        [Production($"NtAliasExpr2: Identifier As [d] NtType Identifier")]
+        public object NtAliasExpr2(Token<Issue540Token> a, object b, Token<Issue540Token> v) => null;
+
+        [Production($"NtAliasExpr3: Identifier As [d] NtType")]
+        public object NtAliasExpr3(Token<Issue540Token> a, object b) => null;
+
+        [Production($"NtDeclarationExpr: [NtDeclarationExpr1 | NtAssignmentExpr]")]
+        public object NtDeclarationExpr(object a) => null;
+
+        [Production($"NtDeclarationExpr1: NtDeclarationModifiersCombined? NtType Identifier NtAssignmentPrime?")]
+        public object NtDeclarationExpr1(ValueOption<object> a, object b, Token<Issue540Token> c,
+            ValueOption<object> d) => null;
+
+        [Production($"NtDeclarationModifiersCombined: NtDeclarationModifier+")]
+        public object NtDeclarationModifiersCombined(List<object> a) => null;
+
+        [Production($"NtDeclarationModifier: [Ref | Readonly | Frozen | Immut]")]
+        public object NtDeclarationModifier(Token<Issue540Token> a) => null;
+
+        [Production($"NtFunctionArgDeclModifier: [Ref | Readonly | Frozen | Immut | Copy]")]
+        public object NtFunctionArgDeclModifier(Token<Issue540Token> a) => null;
+
+        [Production($"NtFunctionArgDeclModifiersCombined: NtFunctionArgDeclModifier+")]
+        public object NtFunctionArgDeclModifiersCombined(List<object> a) => null;
+
+        [Production($"NtAssignmentPrime: Equals NtExpression")]
+        public object NtAssignmentPrime(Token<Issue540Token> a, object b) => null;
+
+        [Production($"NtAssignmentExpr: NtAssignmentExpr1")]
+        public object NtAssignmentExpr(object a) => null;
+
+        [Production($"NtAssignmentExpr1: Issue540Parser_expressions")]
+        public object NtAssignmentExpr1(object a) => null;
+
+        [Operand]
+        [Production($"NtPrimary: NtLPrimary NtPrimaryPrime?")]
+        public object NtPrimary(object a, ValueOption<object> b) => null;
+
+        [Production($"NtPrimaryPrime: [NtIndexPrime | NtFunctionCallPrime]")]
+        public object NtPrimaryPrime(object a) => null;
+
+        [Production($"NtIndexPrime: OpenSquare [d] NtExpression CloseSquare [d]")]
+        public object NtIndexPrime(object a) => null;
+
+        [Production($"NtLPrimary: [NtNewExpr | NtLPrimary1 | NtLPrimary2 | NtLPrimary3]")]
+        public object NtLPrimary(object a) => null;
+
+        [Production($"NtLPrimary1: OpenParen [d] NtExpression CloseParen [d]")]
+        public object NtLPrimary1(object a) => null;
+
+        [Production($"NtLPrimary2: Copy [d] NtExpression")]
+        public object NtLPrimary2(object a) => null;
+
+        [Production($"NtLPrimary3: [Identifier | Number | String | TrueLiteral | FalseLiteral]")]
+        public object NtLPrimary3(Token<Issue540Token> a) => null;
+
+        [Production($"NtNewExpr: New [d] NtType OpenParen [d] NtArgList?")]
+        public object NtNewExpr(object a, ValueOption<object> b) => null;
+
+        [Production($"NtFunctionCallPrime:OpenParen [d] NtArgList? CloseParen [d]")]
+        public object NtFunctionCallPrime(ValueOption<object> a) => null;
+
+        [Production($"NtArgList: NtArgListElement NtArgListPrime*")]
+        public object NtArgList(object a, List<object> b) => null;
+
+        [Production($"NtArgListElement: NtArgumentLabel? NtExpression")]
+        public object NtArgListElement(ValueOption<object> a, object b) => null;
+
+        [Production($"NtArgListPrime: Comma [d] NtArgListElement")]
+        public object NtArgListPrime(object a) => null;
+
+        [Production($"NtArgumentLabel: Identifier Colon [d]")]
+        public object NtArgumentLabel(Token<Issue540Token> ident) => null;
+
+        [Production($"NtTypeCSV: NtType (Comma [d] NtType)*")]
+        public object NtTypeCsv(object aType, List<Group<Issue540Token, object>> otherTypes) => null;
+
+        [Production($"NtType: [NtBaseType | NtGenericType]")]
+        public object NtType(object node) => null;
+
+        [Production(
+            $"NtGenericType: [TypeArray | TypeList | TypeSet | TypeDict | TypeCollection] OpenAngleSquare [d] NtTypeCSV CloseAngleSquare [d]")]
+        public object NtGenericType(Token<Issue540Token> typeToken, object typeArgs) => null;
+
+        [Production(
+            $"NtBaseType: [TypeByte | TypeShort | TypeInt | TypeLong | TypeLongInt | TypeFloat | TypeDouble | TypeRational | TypeNumber | TypeString | TypeChar | TypeVoid]")]
+        public object NtBaseType(Token<Issue540Token> typeToken) => null;
+
+        #region ComparisonExpressions
+
+        const int EqualToPrecedence = NotExprPrecedence + 1;
+        const int NotEqualToPrecedence = EqualToPrecedence;
+        const int GreaterThanPrecedence = NotEqualToPrecedence;
+        const int LessThanPrecedence = GreaterThanPrecedence;
+        const int GreaterThanOrEqualToPrecedence = LessThanPrecedence;
+        const int LessThanOrEqualToPrecedence = GreaterThanOrEqualToPrecedence;
+
+        [Infix((int)Issue540Token.EqualTo, Associativity.Right, EqualToPrecedence)]
+        [Infix((int)Issue540Token.NotEqualTo, Associativity.Right, NotEqualToPrecedence)]
+        [Infix((int)Issue540Token.GreaterThan, Associativity.Right, GreaterThanPrecedence)]
+        [Infix((int)Issue540Token.LessThan, Associativity.Right, LessThanPrecedence)]
+        [Infix((int)Issue540Token.GreaterThanOrEqualTo, Associativity.Right, GreaterThanOrEqualToPrecedence)]
+        [Infix((int)Issue540Token.LessThanOrEqualTo, Associativity.Right, LessThanOrEqualToPrecedence)]
+        public object ComparisonExpressions(object a, Token<Issue540Token> b, object c) => null;
+
+        #endregion
+
+        #region OtherExpressions
+
+        const int AssignmentExprPrecedence = 1;
+        const int ImpliesExprPrecedence = AssignmentExprPrecedence + 1;
+        const int OrExprPrecedence = ImpliesExprPrecedence + 1;
+
+        const int XorExprPrecedence = OrExprPrecedence + 1;
+
+        const int AndExprPrecedence = XorExprPrecedence + 1;
+
+        const int NotExprPrecedence = AndExprPrecedence + 1;
+        const int AdditionPrecedence = EqualToPrecedence + 1;
+        const int SubtractionPrecedence = AdditionPrecedence;
+
+        const int MultiplicationPrecedence = SubtractionPrecedence + 1;
+        const int DivisionPrecedence = MultiplicationPrecedence;
+
+        const int PowerPrecedence = DivisionPrecedence + 1;
+
+        const int NegationPrecedence = PowerPrecedence + 1;
+
+        const int FactorialPrecedence = NegationPrecedence + 1;
+        const int RShiftPrecedence = FactorialPrecedence + 1;
+        const int LShiftPrecedence = RShiftPrecedence + 1;
+        const int BitwiseOrExprPrecedence = LShiftPrecedence + 1;
+
+        const int BitwiseXorExprPrecedence = BitwiseOrExprPrecedence + 1;
+
+        const int BitwiseAndExprPrecedence = BitwiseXorExprPrecedence + 1;
+
+        const int BitwiseNotExprPrecedence = BitwiseAndExprPrecedence + 1;
+
+        #endregion
+
+        [Postfix((int)Issue540Token.Factorial, Associativity.Left, FactorialPrecedence)]
+        public object Factorial(object a, Token<Issue540Token> b) => null;
+
+        [Prefix((int)Issue540Token.LogicalNot, Associativity.Right, NotExprPrecedence)]
+        [Prefix((int)Issue540Token.BitwiseNegation, Associativity.Right, BitwiseNotExprPrecedence)]
+        [Prefix((int)Issue540Token.Subtraction, Associativity.Right, NegationPrecedence)]
+        public object Prefix(Token<Issue540Token> a, object b) => null;
+
+
+        [Infix((int)Issue540Token.Equals, Associativity.Right, 1)]
+        [Infix((int)Issue540Token.LogicalOr, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.LogicalXor, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.LogicalAnd, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.Addition, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.Subtraction, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.Division, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.Multiplication, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.Exponentiation, Associativity.Right, 1)]
+        [Infix((int)Issue540Token.Subtraction, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.BitwiseOr, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.BitwiseXor, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.BitwiseAnd, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.BitwiseLeftShift, Associativity.Left, 1)]
+        [Infix((int)Issue540Token.BitwiseRightShift, Associativity.Left, 1)]
+        public object BinOp(object left, Token<Issue540Token> a, object b) => null;
+    }
+}
\ No newline at end of file
diff --git a/tests/ParserTests/Issue540/Issue540Token.cs b/tests/ParserTests/Issue540/Issue540Token.cs
new file mode 100644
index 00000000..7321e481
--- /dev/null
+++ b/tests/ParserTests/Issue540/Issue540Token.cs
@@ -0,0 +1,154 @@
+using System.ComponentModel.DataAnnotations;
+using sly.lexer;
+
+namespace ParserTests.Issue540
+{
+    public enum Issue540Token
+    {
+        EOF,
+
+        //should be shared between all sets of valid tokens, since invalid ones will simply be unused
+        [Lexeme(GenericToken.Int)] [Lexeme(GenericToken.Double)]
+        Number,
+
+        [Lexeme(GenericToken.Identifier, IdentifierType.Custom, "_A-Za-z", "_0-9A-Za-z")]
+        Identifier,
+
+        [Lexeme(GenericToken.String)] [Lexeme(GenericToken.String, "'")]
+        String,
+
+        //Operators
+
+        #region bitwise operator
+
+        [Sugar("&")] BitwiseAnd,
+        [Sugar("|")] BitwiseOr,
+        [Sugar("^")] BitwiseXor,
+        [Sugar("<<")] BitwiseLeftShift,
+        [Sugar(">>")] BitwiseRightShift,
+        [Sugar("~")] BitwiseNegation,
+
+        #endregion
+
+        #region arithmetic operator
+
+        [Sugar("+")] Addition,
+        [Sugar("-")] Subtraction,
+        [Sugar("*")] Multiplication,
+        [Sugar("/")] Division,
+        [Sugar("**")] Exponentiation,
+        [Sugar("!")] Factorial,
+
+        #endregion
+
+        #region logical operator
+
+        [Keyword("and")] LogicalAnd,
+        [Keyword("or")] LogicalOr,
+        [Keyword("not")] LogicalNot,
+        [Keyword("xor")] LogicalXor,
+        [Keyword("implies")] LogicalImplies,
+
+        #endregion
+
+        #region Brackets
+
+        [Sugar("(")] OpenParen,
+        [Sugar(")")] CloseParen,
+        [Sugar("{")] OpenCurly,
+        [Sugar("}")] CloseCurly,
+        [Sugar("[")] OpenSquare,
+        [Sugar("]")] CloseSquare,
+        [Sugar("<[")] OpenAngleSquare,
+        [Sugar("]>")] CloseAngleSquare,
+
+        #endregion
+
+        #region Symbols
+
+        [Sugar(",")] Comma,
+        [Sugar(":")] Colon,
+        [Sugar(".")] Dot,
+
+        #endregion
+
+        #region Comparison_Operator
+
+        [Sugar("==")] EqualTo,
+        [Sugar("!=")] NotEqualTo,
+        [Sugar(">")] GreaterThan,
+        [Sugar("<")] LessThan,
+        [Sugar(">=")] GreaterThanOrEqualTo,
+        [Sugar("<=")] LessThanOrEqualTo,
+        [Keyword("is")] ComparisonIs,
+        [Keyword("in")] In,
+        [Sugar(";")] Semicolon,
+
+        #endregion
+
+        [Sugar("=")] Equals,
+
+        #region Types
+
+        [Keyword("float")] TypeFloat,
+        [Keyword("int")] TypeInt,
+        [Keyword("double")] TypeDouble,
+
+        [Keyword("number")] [Keyword("bigfloat")]
+        TypeNumber,
+        [Keyword("long")] TypeLong,
+
+        [Keyword("longint")] [Keyword("bigint")]
+        TypeLongInt,
+        [Keyword("byte")] TypeByte,
+        [Keyword("array")] TypeArray,
+        [Keyword("list")] TypeList,
+        [Keyword("set")] TypeSet,
+        [Keyword("dict")] TypeDict,
+        [Keyword("short")] TypeShort,
+        [Keyword("rational")] TypeRational,
+        [Keyword("string")] TypeString,
+        [Keyword("char")] TypeChar,
+        [Keyword("void")] TypeVoid,
+
+        #endregion
+
+        #region control-flow
+
+        [Keyword("return")] Return,
+        [Keyword("break")] Break,
+        [Keyword("continue")] Continue,
+        [Keyword("if")] If,
+        [Keyword("else")] Else,
+        [Keyword("switch")] Switch,
+
+        #endregion
+
+        #region Loops
+
+        [Keyword("for")] For,
+        [Keyword("while")] While,
+
+        #endregion
+
+        [Keyword("as")] As,
+
+        #region FunctionMod
+
+        [Keyword("cascading")] Cascading,
+        [Keyword("copy")] Copy,
+        [Keyword("readonly")] Readonly,
+        [Keyword("frozen")] Frozen,
+        [Keyword("immut")] Immut,
+        [Keyword("ref")] Ref,
+        [Keyword("new")] New,
+
+        #endregion
+
+        [Keyword("true")] TrueLiteral,
+        [Keyword("false")] FalseLiteral,
+        [Keyword("collection")] TypeCollection,
+        [Comment("#", "/*", "*/")] Comment
+
+    }
+}
\ No newline at end of file
diff --git a/tests/ParserTests/IssuesTests.cs b/tests/ParserTests/IssuesTests.cs
index b61715bc..f9de9095 100644
--- a/tests/ParserTests/IssuesTests.cs
+++ b/tests/ParserTests/IssuesTests.cs
@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using System.Linq;
 using NFluent;
 using ParserTests.Issue218;
@@ -7,6 +8,7 @@
 using ParserTests.Issue260;
 using ParserTests.Issue277;
 using ParserTests.Issue536;
+using ParserTests.Issue540;
 using SlowEOS;
 using sly.buildresult;
 using sly.lexer;
@@ -135,6 +137,18 @@ public static void Issue536Test()
             Check.That(equals.TokenID).IsEqualTo(Token536.Equals);
             var x = Token536.Equals;
         }
+   
+        [Fact]
+        public static void Issue540Test()
+        {
+            ParserBuilder<Issue540Token, object> builder = new ParserBuilder<Issue540Token, object>();
+            var buildParser = builder.BuildParser(new Issue540Parser(), ParserType.EBNF_LL_RECURSIVE_DESCENT, "NtSCExpr");
+            Check.That(buildParser).IsOk();
+            
+            var parser = buildParser.Result;
+            var parsed = parser.Parse("1;");            
+            Check.That(parsed).IsOkParsing(checkIfResultisNull:false);
+        }
     }
 
    
diff --git a/tests/ParserTests/NFluentParseExtensions.cs b/tests/ParserTests/NFluentParseExtensions.cs
index 158429a0..5c2cd6ef 100644
--- a/tests/ParserTests/NFluentParseExtensions.cs
+++ b/tests/ParserTests/NFluentParseExtensions.cs
@@ -11,11 +11,11 @@ namespace ParserTests
 {
     public static class NFluentParseExtensions
     {
-        public static ICheckLink<ICheck<ParseResult<IN,OUT>>> IsOkParsing<IN,OUT>(this ICheck<ParseResult<IN,OUT>> context) where IN : struct
+        public static ICheckLink<ICheck<ParseResult<IN,OUT>>> IsOkParsing<IN,OUT>(this ICheck<ParseResult<IN,OUT>> context, bool checkIfResultisNull = true) where IN : struct
         {
             ExtensibilityHelper.BeginCheck(context)
                 .FailWhen(sut => sut.IsError, $"parse failed")
-                .FailWhen(sut => sut.Result == null  && !sut.SyntaxTree.IsEpsilon, "parse result is null")
+                .FailWhen(sut => sut.Result == null  && checkIfResultisNull && !sut.SyntaxTree.IsEpsilon, "parse result is null")
                 .OnNegate("parse expected to fail.")
                 .EndCheck();
             return ExtensibilityHelper.BuildCheckLink(context);