diff --git a/ParserTests/Issue251/LexerAndParser.cs b/ParserTests/Issue251/LexerAndParser.cs
new file mode 100644
index 00000000..5643efd1
--- /dev/null
+++ b/ParserTests/Issue251/LexerAndParser.cs
@@ -0,0 +1,140 @@
+
+    using System;
+using System.Data;
+using System.Text;
+using sly.lexer;
+using sly.parser.generator;
+    namespace ParserTests.Issue251
+    {
+
+    public class Issue251Parser
+    {
+        public enum Issue251Tokens
+        {
+            [Lexeme("[0-9][0-9]*")] DIGITS,
+
+            [Lexeme("\"[^\"\\\\]*(\\\\.[^\"\\\\])*\"")]
+            LITERAL_STRING, // "[^"\\]*(\\.[^"\\]*)*"  , which allowing escaped quotes in string. 
+            [Lexeme("[a-zA-Z_][0-9a-zA-Z_]*")] IDENTIFIER,
+            [Lexeme("\\+")] OP_PLUS,
+            [Lexeme("-")] OP_MINUS,
+            [Lexeme("\\*")] OP_MULTIPLY,
+            [Lexeme("/")] OP_DIVIDE,
+            [Lexeme("%")] OP_MODULE,
+            [Lexeme("(")] PARENTHESIS_L,
+            [Lexeme(")")] PARENTHESIS_R,
+
+            [Lexeme("[ \\t][ \\t]*", isSkippable: true)]
+            IGNORED, // simply discarded in lexer
+        }
+
+        public class ExprClosure
+        {
+            public enum Types
+            {
+                INT,
+                STRING
+            }
+
+            public Types ResultType;
+
+            // C# doesn't have std::any or std::variant. Fuck it. 
+            public int valueInt;
+            public string valueString;
+        }
+
+        private void SyntaxCheck(bool what, string msg = "")
+        {
+            if (!what)
+                throw new SyntaxErrorException("Syntax error: " + msg);
+        }
+
+        /*
+         * RnLang is a script language, so the input expressions
+         *   are directly evaluated in parser.
+         *
+         * int ::= DIGITS
+         * string ::= LITERAL_STRING
+         * expr ::= int | string
+         * expr ::= expr OP_PLUS expr
+         * expr ::= expr OP_MINUS expr
+         * expr ::= expr OP_MULTIPLY expr
+         * expr ::= expr OP_DIVIDE expr
+         * expr ::= expr OP_MODULE expr
+         * expr ::= IDENTIFIER PARENTHESIS_L expr PARENTHESIS_R
+         * expr ::= PARENTHESIS_L expr PARENTHESIS_R
+         */
+        [Production("int: DIGITS")]
+        public int exprIntL(Token<Issue251Tokens> expr) => expr.IntValue;
+
+        [Production("string: LITERAL_STRING")]
+        public string exprStringL(Token<Issue251Tokens> expr) => 
+            expr.StringWithoutQuotes.Replace("\\\"", "\""); // default string delimiter works. 
+
+        [Production("expr: int")]
+        public ExprClosure exprInt(int what) =>
+            new ExprClosure() {ResultType = ExprClosure.Types.INT, valueInt = what};
+
+        [Production("expr: string")]
+        public ExprClosure exprString(string what) =>
+            new ExprClosure() {ResultType = ExprClosure.Types.STRING, valueString = what};
+
+        [Production("expr: expr OP_PLUS expr")]
+        public ExprClosure exprAdd(ExprClosure l, Token<Issue251Tokens> _, ExprClosure r)
+        {
+            SyntaxCheck(l.ResultType == r.ResultType, "Type error: expected int + int or string + string");
+            switch (l.ResultType)
+            {
+                case ExprClosure.Types.INT:
+                    l.valueInt += r.valueInt;
+                    return l;
+                case ExprClosure.Types.STRING:
+                    l.valueString += r.valueString;
+                    return l;
+            }
+            throw new ArgumentException("Internal Error");
+        }
+
+        [Production("expr: expr OP_MINUS expr")]
+        public ExprClosure exprMin(ExprClosure l, Token<Issue251Tokens> _, ExprClosure r)
+        {
+            SyntaxCheck(l.ResultType == ExprClosure.Types.INT, "Type error: expected int - int");
+            SyntaxCheck(r.ResultType == ExprClosure.Types.INT, "Type error: expected int - int");
+            l.valueInt -= r.valueInt;
+            return l;
+        }
+
+        [Production("expr: expr OP_MULTIPLY expr")]
+        public ExprClosure exprMul(ExprClosure l, Token<Issue251Tokens> _, ExprClosure r)
+        {
+            SyntaxCheck(r.ResultType == ExprClosure.Types.INT, "Syntax error: expected ? * int");
+            switch (l.ResultType)
+            {
+                case ExprClosure.Types.INT:
+                    l.valueInt *= r.valueInt;
+                    return l;
+                case ExprClosure.Types.STRING:
+                    l.valueString = new StringBuilder().Insert(0, l.valueString, r.valueInt).ToString();
+                    return l;
+            }
+            throw new ArgumentException("Internal Error");
+        }
+
+        // [Production("expr: int OP_DIVIDE expr")]
+        // public ExprClosure exprDiv(int l, Token<LexerTokens> _, ExprClosure r)
+        // {
+        //     SyntaxCheck(r.ResultType == ExprClosure.Types.INT, "Syntax error: expected int / int, got int / string");
+        //     r.valueInt = l / r.valueInt;
+        //     return r;
+        // }
+
+        // [Production("expr: int OP_MODULE expr")]
+        // public ExprClosure exprImod(int l, Token<LexerTokens> _, ExprClosure r)
+        // {
+        //     SyntaxCheck(r.ResultType == ExprClosure.Types.INT, "Syntax error: expected int % int, got int % string");
+        //     r.valueInt = l % r.valueInt;
+        //     return r;
+        // }
+    }
+}
+
diff --git a/ParserTests/IssuesTests.cs b/ParserTests/IssuesTests.cs
index 3028a065..50bcc25f 100644
--- a/ParserTests/IssuesTests.cs
+++ b/ParserTests/IssuesTests.cs
@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using ParserTests.Issue251;
+using sly.buildresult;
 using sly.lexer;
 using sly.parser.generator;
 using Xunit;
@@ -206,5 +208,16 @@ public static void Issue219BNF()
             var exception = Assert.Throws<Exception219>(() => parser.Parse("a = 1"));
             Assert.Equal("visitor error",exception.Message);                
         }
+        
+        [Fact]
+        public static void Issue251LeftrecForBNF() {
+            ParserBuilder<Issue251Parser.Issue251Tokens,Issue251Parser.ExprClosure> builder = new ParserBuilder<Issue251Parser.Issue251Tokens, Issue251Parser.ExprClosure>();
+            Issue251Parser instance = new Issue251Parser();
+            var bres = builder.BuildParser(instance,ParserType.LL_RECURSIVE_DESCENT, "expr");
+            Assert.False(bres.IsOk);
+            Assert.Equal(1,bres.Errors.Count);
+            var error = bres.Errors.First();
+            Assert.Equal(ErrorCodes.PARSER_LEFT_RECURSIVE, error.Code);
+        }
     }
 }
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