diff --git a/LiteDB/Document/Expression/BsonExpression.cs b/LiteDB/Document/Expression/BsonExpression.cs
index 45793ab4e..eb52a77a1 100644
--- a/LiteDB/Document/Expression/BsonExpression.cs
+++ b/LiteDB/Document/Expression/BsonExpression.cs
@@ -414,14 +414,14 @@ internal static void SetParameters(BsonExpression expr, BsonDocument parameters)
         /// </summary>
         private static Dictionary<string, MethodInfo> _methods =
             typeof(BsonExpressionMethods).GetMethods(BindingFlags.Public | BindingFlags.Static)
-            .ToDictionary(m => m.Name.ToUpper() + "~" + m.GetParameters().Where(p => p.ParameterType != typeof(Collation)).Count());
+            .ToDictionary(m => m.Name.ToUpperInvariant() + "~" + m.GetParameters().Where(p => p.ParameterType != typeof(Collation)).Count());
 
         /// <summary>
         /// Get expression method with same name and same parameter - return null if not found
         /// </summary>
         internal static MethodInfo GetMethod(string name, int parameterCount)
         {
-            var key = name.ToUpper() + "~" + parameterCount;
+            var key = name.ToUpperInvariant() + "~" + parameterCount;
 
             return _methods.GetOrDefault(key);
         }
@@ -440,7 +440,7 @@ internal static MethodInfo GetMethod(string name, int parameterCount)
         /// </summary>
         private static Dictionary<string, MethodInfo> _functions =
             typeof(BsonExpressionFunctions).GetMethods(BindingFlags.Public | BindingFlags.Static)
-            .ToDictionary(m => m.Name.ToUpper() + "~" + m.GetParameters()
+            .ToDictionary(m => m.Name.ToUpperInvariant() + "~" + m.GetParameters()
             .Skip(5).Count());
 
         /// <summary>
@@ -448,7 +448,7 @@ internal static MethodInfo GetMethod(string name, int parameterCount)
         /// </summary>
         internal static MethodInfo GetFunction(string name, int parameterCount = 0)
         {
-            var key = name.ToUpper() + "~" + parameterCount;
+            var key = name.ToUpperInvariant() + "~" + parameterCount;
 
             return _functions.GetOrDefault(key);
         }
diff --git a/LiteDB/Document/Expression/Parser/BsonExpressionParser.cs b/LiteDB/Document/Expression/Parser/BsonExpressionParser.cs
index 6817d7180..77ca4afe5 100644
--- a/LiteDB/Document/Expression/Parser/BsonExpressionParser.cs
+++ b/LiteDB/Document/Expression/Parser/BsonExpressionParser.cs
@@ -121,7 +121,7 @@ public static BsonExpression ParseFullExpression(Tokenizer tokenizer, Expression
                 }
 
                 values.Add(expr);
-                ops.Add(op.ToUpper());
+                ops.Add(op.ToUpperInvariant());
             }
 
             var order = 0;
@@ -888,7 +888,7 @@ private static BsonExpression TryParseMethodCall(Tokenizer tokenizer, Expression
             var useSource = false;
             var fields = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
 
-            src.Append(token.Value.ToUpper() + "(");
+            src.Append(token.Value.ToUpperInvariant() + "(");
 
             // method call with no parameters
             if (tokenizer.LookAhead().Type == TokenType.CloseParenthesis)
@@ -926,7 +926,7 @@ private static BsonExpression TryParseMethodCall(Tokenizer tokenizer, Expression
 
             var method = BsonExpression.GetMethod(token.Value, pars.Count);
 
-            if (method == null) throw LiteException.UnexpectedToken($"Method '{token.Value.ToUpper()}' does not exist or contains invalid parameters", token);
+            if (method == null) throw LiteException.UnexpectedToken($"Method '{token.Value.ToUpperInvariant()}' does not exist or contains invalid parameters", token);
 
             // test if method are decorated with "Variable" (immutable = false)
             if (method.GetCustomAttribute<VolatileAttribute>() != null)
@@ -1170,7 +1170,7 @@ private static BsonExpression TryParseFunction(Tokenizer tokenizer, ExpressionCo
             if (tokenizer.Current.Type != TokenType.Word) return null;
             if (tokenizer.LookAhead().Type != TokenType.OpenParenthesis) return null;
 
-            var token = tokenizer.Current.Value.ToUpper();
+            var token = tokenizer.Current.Value.ToUpperInvariant();
 
             switch (token)
             {
@@ -1385,7 +1385,7 @@ private static string ReadOperant(Tokenizer tokenizer)
 
             if (token.Is("ALL") || token.Is("ANY"))
             {
-                var key = token.Value.ToUpper();
+                var key = token.Value.ToUpperInvariant();
 
                 tokenizer.ReadToken(); // consume operant
 
@@ -1474,7 +1474,7 @@ internal static BsonExpression CreateLogicExpression(BsonExpressionType type, Bs
                 Expression = Expression.New(ctor, expr),
                 Left = left,
                 Right = right,
-                Source = left.Source + " " + (type.ToString().ToUpper()) + " " + right.Source
+                Source = left.Source + " " + (type.ToString().ToUpperInvariant()) + " " + right.Source
             };
 
             return result;
diff --git a/LiteDB/Utils/Collation.cs b/LiteDB/Utils/Collation.cs
index 844737632..0ccc29e79 100644
--- a/LiteDB/Utils/Collation.cs
+++ b/LiteDB/Utils/Collation.cs
@@ -70,15 +70,6 @@ public int Compare(string left, string right)
             return result < 0 ? -1 : result > 0 ? +1 : 0;
         }
 
-        /// <summary>
-        /// Compare 2 chars values using current culture/compare options
-        /// </summary>
-        public int Compare(char left, char right)
-        {
-            //TODO implementar o compare corretamente
-            return char.ToUpper(left) == char.ToUpper(right) ? 0 : 1;
-        }
-
         public int Compare(BsonValue left, BsonValue rigth)
         {
             return left.CompareTo(rigth, this);
diff --git a/LiteDB/Utils/Extensions/StringExtensions.cs b/LiteDB/Utils/Extensions/StringExtensions.cs
index 468dcd3c4..12270ee39 100644
--- a/LiteDB/Utils/Extensions/StringExtensions.cs
+++ b/LiteDB/Utils/Extensions/StringExtensions.cs
@@ -108,7 +108,7 @@ public static bool SqlLike(this string str, string pattern, Collation collation)
 
                 if (isWildCardOn)
                 {
-                    if (char.ToUpper(c) == char.ToUpper(p))
+                    if (collation.Compare(c.ToString(), p.ToString()) == 0)
                     {
                         isWildCardOn = false;
                         patternIndex++;
@@ -140,7 +140,7 @@ public static bool SqlLike(this string str, string pattern, Collation collation)
                 }
                 else
                 {
-                    if (collation.Compare(c, p) == 0)
+                    if (collation.Compare(c.ToString(), p.ToString()) == 0)
                     {
                         patternIndex++;
                     }