diff --git a/CSharp.lua/CoreSystem.Lua/CoreSystem/Char.lua b/CSharp.lua/CoreSystem.Lua/CoreSystem/Char.lua
index b0ae7d24..463d93c2 100644
--- a/CSharp.lua/CoreSystem.Lua/CoreSystem/Char.lua
+++ b/CSharp.lua/CoreSystem.Lua/CoreSystem/Char.lua
@@ -73,6 +73,10 @@ local function get(s, index)
   return c
 end
 
+local function isAsciiLetter(c)
+  return (c >= 65 and c <= 90) or (c >= 97 and c <= 122)
+end
+
 local function isDigit(c, index)
   if index then
     c = get(c, index)
@@ -86,7 +90,7 @@ local function isLetter(c, index)
     c = get(c, index)
   end
   if c < 128 then
-    return (c >= 65 and c <= 90) or (c >= 97 and c <= 122)
+    return isAsciiLetter(c)
   else
     return (c >= 0x0400 and c <= 0x042F)
       or (c >= 0x03AC and c <= 0x03CE)
@@ -107,6 +111,7 @@ local Char = System.defStc("System.Char", {
   EqualsObj = Int.EqualsObj,
   GetHashCode = Int.GetHashCode,
   default = Int.default,
+  IsAsciiLetter = isAsciiLetter,
   IsControl = function (c, index)
     if index then
       c = get(c, index)
diff --git a/test/BridgeNetTests/Batch1/src/SimpleTypes/CharTests.cs b/test/BridgeNetTests/Batch1/src/SimpleTypes/CharTests.cs
index 530dc424..9880b63a 100644
--- a/test/BridgeNetTests/Batch1/src/SimpleTypes/CharTests.cs
+++ b/test/BridgeNetTests/Batch1/src/SimpleTypes/CharTests.cs
@@ -329,5 +329,20 @@ public void IsLetterWithStringAndIndexWorks()
 #endif
             Assert.False(char.IsLetter("0" + '\u0100', 0), "#10");
         }
+
+        [Test]
+        public void IsAsciiLetterWorks()
+        {
+            Assert.True(char.IsAsciiLetter('A'), "Should match uppercase letter (first)");
+            Assert.True(char.IsAsciiLetter('Z'), "Should match uppercase letter (last)");
+            Assert.True(char.IsAsciiLetter('a'), "Should match lowercase letter (first)");
+            Assert.True(char.IsAsciiLetter('z'), "Should match lowercase letter (last)");
+
+            Assert.False(char.IsAsciiLetter('@'), "Should not match character before 'A'");
+            Assert.False(char.IsAsciiLetter('['), "Should not match character after 'Z'");
+            Assert.False(char.IsAsciiLetter('`'), "Should not match character before 'a'");
+            Assert.False(char.IsAsciiLetter('{'), "Should not match character after 'z'");
+            Assert.False(char.IsAsciiLetter('0'), "Should not match digit");
+        }
     }
 }