diff --git a/Yolol.Cylon/Deserialisation/Versions/V_0_3_0.cs b/Yolol.Cylon/Deserialisation/Versions/V_0_3_0.cs
index f5efca2..b04b44c 100644
--- a/Yolol.Cylon/Deserialisation/Versions/V_0_3_0.cs
+++ b/Yolol.Cylon/Deserialisation/Versions/V_0_3_0.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Linq;
 using Newtonsoft.Json.Linq;
 using Semver;
@@ -132,7 +133,7 @@ private BaseExpression ParseExpression(JToken jtok)
                     return ParseUnaryExpression(jtok);
 
                 case "expression::number":
-                    return new ConstantNumber((Number)decimal.Parse(jtok.Value<string>("num")));
+                    return new ConstantNumber((Number)decimal.Parse(jtok.Value<string>("num"), CultureInfo.InvariantCulture));
 
                 case "expression::string":
                     return new ConstantString(jtok.Value<string>("str"));
diff --git a/Yolol.Cylon/Deserialisation/Versions/V_1_X_X.cs b/Yolol.Cylon/Deserialisation/Versions/V_1_X_X.cs
index c9766c5..e8041fc 100644
--- a/Yolol.Cylon/Deserialisation/Versions/V_1_X_X.cs
+++ b/Yolol.Cylon/Deserialisation/Versions/V_1_X_X.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Linq;
 using Newtonsoft.Json.Linq;
 using Yolol.Execution;
@@ -192,7 +193,7 @@ BaseExpression ParseModify(string op)
                     return ParseModify(type[2]);
 
                 case "number":
-                    return new ConstantNumber((Number)decimal.Parse(jtok.Value<string>("num")));
+                    return new ConstantNumber((Number)decimal.Parse(jtok.Value<string>("num"), CultureInfo.InvariantCulture));
 
                 case "string":
                     return new ConstantString(jtok.Value<string>("str"));
diff --git a/Yolol/Execution/Number.cs b/Yolol/Execution/Number.cs
index 5bd8ad1..bbb3e62 100644
--- a/Yolol/Execution/Number.cs
+++ b/Yolol/Execution/Number.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.Runtime.CompilerServices;
 using Yolol.Execution.Attributes;
 
@@ -124,13 +125,13 @@ public override int GetHashCode()
         public static Number Parse(string s)
         {
             // First check if the number is out of the valid range
-            var d = double.Parse(s);
+            var d = double.Parse(s, CultureInfo.InvariantCulture);
             if (d >= MaxValue._value)
                 return MaxValue;
             else if (d <= MinValue._value)
                 return MinValue;
 
-            return (Number)decimal.Parse(s);
+            return (Number)decimal.Parse(s, CultureInfo.InvariantCulture);
         }
 
         public static explicit operator Number(bool b)
diff --git a/Yolol/Grammar/Parser.cs b/Yolol/Grammar/Parser.cs
index 4e54378..a559b7f 100644
--- a/Yolol/Grammar/Parser.cs
+++ b/Yolol/Grammar/Parser.cs
@@ -16,7 +16,7 @@ public static Result<Program, ParseError> ParseProgram(string program)
             catch (FormatException e)
             {
                 var c = e.Data["cursor"] as Cursor;
-                return new Result<Program, ParseError>(new ParseError(c!, e.Message));
+                return new Result<Program, ParseError>(new ParseError(c, e.Message));
             }
         }
 
@@ -65,10 +65,10 @@ public Result(TErr err)
 
         public class ParseError
         {
-            public Cursor Cursor { get; }
+            public Cursor? Cursor { get; }
             public string Message { get; }
 
-            public ParseError(Cursor cursor, string message)
+            public ParseError(Cursor? cursor, string message)
             {
                 message = message
                     .Replace("\r", "\\r")
@@ -80,6 +80,9 @@ public ParseError(Cursor cursor, string message)
 
             public override string ToString()
             {
+                if (Cursor == null)
+                    return Message;
+
                 var spaces = new string(' ', Math.Max(0, Cursor.Column - 2));
 
                 return $"{Cursor.Subject}\n"
diff --git a/Yolol/Yolol.csproj b/Yolol/Yolol.csproj
index e1de5f1..beb366b 100644
--- a/Yolol/Yolol.csproj
+++ b/Yolol/Yolol.csproj
@@ -9,7 +9,7 @@
     <PackageProjectUrl>https://github.com/martindevans/Yolol</PackageProjectUrl>
     <RepositoryUrl>https://github.com/martindevans/Yolol</RepositoryUrl>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
-    <Version>13.0.0</Version>
+    <Version>13.0.1</Version>
     <LangVersion>8.0</LangVersion>
     <Nullable>enable</Nullable>
     <Platforms>AnyCPU;x64</Platforms>
diff --git a/YololEmulator.Tests/Ladder/PrimeCountingFunction.cs b/YololEmulator.Tests/Ladder/PrimeCountingFunction.cs
new file mode 100644
index 0000000..40729d8
--- /dev/null
+++ b/YololEmulator.Tests/Ladder/PrimeCountingFunction.cs
@@ -0,0 +1,59 @@
+using System;
+using System.Collections.Generic;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Yolol.Execution;
+
+namespace YololEmulator.Tests.Ladder
+{
+    [TestClass]
+    public class PrimeCountingFunction
+        : BaseGenerator
+    {
+        private readonly Dictionary<int, bool> _cache = new();
+
+        [TestMethod]
+        public void Generate()
+        {
+            Run(34923, 10000, false, Generator.ScoreMode.BasicScoring);
+        }
+
+        protected override bool GenerateCase(Random random, int index, Dictionary<string, Value> inputs, Dictionary<string, Value> outputs)
+        {
+            var i = index + 1;
+            inputs.Add("i", i);
+            outputs.Add("o", PrimeCount(i));
+            return true;
+        }
+
+        private int PrimeCount(int n)
+        {
+            var count = n >= 2 ? 1 : 0;
+            for (var i = 3; i < n; i += 2)
+                if (IsOddIntPrime(i))
+                    count++;
+            return count;
+        }
+
+        private bool IsOddIntPrime(int number)
+        {
+            if (number <= 1)
+                return false;
+            if (_cache.TryGetValue(number, out var cached))
+                return cached;
+
+            var boundary = (int)Math.Floor(Math.Sqrt(number));
+
+            for (var i = 3; i <= boundary; i += 2)
+            {
+                if (number % i == 0)
+                {
+                    _cache[number] = false;
+                    return false;
+                }
+            }
+
+            _cache[number] = true;
+            return true;        
+        }
+    }
+}
diff --git a/YololEmulator/YololEmulator.csproj b/YololEmulator/YololEmulator.csproj
index 482fd75..ff1997f 100644
--- a/YololEmulator/YololEmulator.csproj
+++ b/YololEmulator/YololEmulator.csproj
@@ -7,7 +7,7 @@
     <LangVersion>8.0</LangVersion>
     <Nullable>enable</Nullable>
     <Platforms>AnyCPU;x64</Platforms>
-    <Version>10.0.0</Version>
+    <Version>10.0.1</Version>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">