diff --git a/Jace/AstBuilder.cs b/Jace/AstBuilder.cs
index 33824b6..24f6bad 100644
--- a/Jace/AstBuilder.cs
+++ b/Jace/AstBuilder.cs
@@ -5,6 +5,7 @@
 using Jace.Execution;
 using Jace.Operations;
 using Jace.Tokenizer;
+using Jace.Util;
 
 namespace Jace
 {
@@ -81,7 +82,7 @@ public Operation Build(IList<Token> tokens)
                             {
                                 if (!caseSensitive)
                                 {
-                                    tokenValue = tokenValue.ToLowerInvariant();
+                                    tokenValue = tokenValue.ToLowerFast();
                                 }
                                 resultStack.Push(new Variable(tokenValue));
                             }
diff --git a/Jace/Execution/ConstantRegistry.cs b/Jace/Execution/ConstantRegistry.cs
index 448a1d0..f934105 100644
--- a/Jace/Execution/ConstantRegistry.cs
+++ b/Jace/Execution/ConstantRegistry.cs
@@ -3,6 +3,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using Jace.Util;
 
 namespace Jace.Execution
 {
@@ -72,7 +73,7 @@ public void RegisterConstant(string constantName, double value, bool isOverWrita
 
         private string ConvertConstantName(string constantName)
         {
-            return caseSensitive ? constantName : constantName.ToLowerInvariant();
+            return caseSensitive ? constantName : constantName.ToLowerFast();
         }
     }
 }
diff --git a/Jace/Execution/FunctionRegistry.cs b/Jace/Execution/FunctionRegistry.cs
index 57de7a2..d976618 100644
--- a/Jace/Execution/FunctionRegistry.cs
+++ b/Jace/Execution/FunctionRegistry.cs
@@ -4,6 +4,7 @@
 using System.Text;
 using System.Reflection;
 using System.Collections;
+using Jace.Util;
 
 namespace Jace.Execution
 {
@@ -112,7 +113,7 @@ public bool IsFunctionName(string functionName)
 
         private string ConvertFunctionName(string functionName)
         {
-            return caseSensitive ? functionName : functionName.ToLowerInvariant();
+            return caseSensitive ? functionName : functionName.ToLowerFast();
         }
     }
 }
diff --git a/Jace/Util/EngineUtil.cs b/Jace/Util/EngineUtil.cs
index 00b1817..612b0c2 100644
--- a/Jace/Util/EngineUtil.cs
+++ b/Jace/Util/EngineUtil.cs
@@ -15,10 +15,32 @@ static internal IDictionary<string, double> ConvertVariableNamesToLowerCase(IDic
             Dictionary<string, double> temp = new Dictionary<string, double>();
             foreach (KeyValuePair<string, double> keyValuePair in variables)
             {
-                temp.Add(keyValuePair.Key.ToLowerInvariant(), keyValuePair.Value);
+                temp.Add(keyValuePair.Key.ToLowerFast(), keyValuePair.Value);
             }
 
             return temp;
         }
+
+        // This is a fast ToLower for strings that are in ASCII
+        static internal string ToLowerFast(this string text)
+        {
+            StringBuilder buffer = new StringBuilder(text.Length);
+
+            for(int i = 0; i < text.Length; i++)
+            {
+                char c = text[i];
+
+                if (c >= 'A' && c <= 'Z')
+                {
+                    buffer.Append((char)(c + 32));
+                }
+                else 
+                {
+                    buffer.Append(c);
+                }
+            }
+
+            return buffer.ToString();
+        }
     }
 }