diff --git a/src/DevToys.Tools.UnitTests/Tools/Helpers/Base64HelperTests.cs b/src/DevToys.Tools.UnitTests/Tools/Helpers/Base64HelperTests.cs
index b78014f9c5..23e84ee9be 100644
--- a/src/DevToys.Tools.UnitTests/Tools/Helpers/Base64HelperTests.cs
+++ b/src/DevToys.Tools.UnitTests/Tools/Helpers/Base64HelperTests.cs
@@ -13,6 +13,7 @@ public class Base64HelperTests
     [InlineData("aGVsbG8gd2f9ybGQ=", false)]
     [InlineData("SGVsbG8gV29y", true)]
     [InlineData("SGVsbG8gVa29y", false)]
+    [InlineData("aGVsbG8gd29ybGQg8J+Xne+4jwo=", true)]
     public void IsValid(string input, bool expectedResult)
     {
         Base64Helper.IsBase64DataStrict(input).Should().Be(expectedResult);
diff --git a/src/DevToys.Tools/Helpers/Base64Helper.cs b/src/DevToys.Tools/Helpers/Base64Helper.cs
index 1f5c835c42..c421f97af7 100644
--- a/src/DevToys.Tools/Helpers/Base64Helper.cs
+++ b/src/DevToys.Tools/Helpers/Base64Helper.cs
@@ -59,9 +59,9 @@ internal static bool IsBase64DataStrict(string? data)
             if (!(current == 0x9
                 || current == 0xA
                 || current == 0xD
-                || current >= 0x20 && current <= 0xD7FF
-                || current >= 0xE000 && current <= 0xFFFD
-                || current >= 0x10000 && current <= 0x10FFFF))
+                || current >= 0x20 && current <= 0xDBFF
+                || current >= 0xDC00 && current <= 0xDFFF
+                || current >= 0xE000 && current <= 0xFFFD))
             {
                 return false;
             }