diff --git a/dart/packages/fory/lib/src/buffer.dart b/dart/packages/fory/lib/src/buffer.dart
index 94f92ca912..dc7af67cc7 100644
--- a/dart/packages/fory/lib/src/buffer.dart
+++ b/dart/packages/fory/lib/src/buffer.dart
@@ -421,7 +421,7 @@ final class Buffer {
   /// Reads an unsigned 64-bit integer written by [writeTaggedUint64].
   int readTaggedUint64() {
     final readIndex = _readerIndex;
-    final first = _view.getInt32(readIndex, Endian.little);
+    final first = _view.getUint32(readIndex, Endian.little);
     if ((first & 1) == 0) {
       _readerIndex = readIndex + 4;
       return first >>> 1;
diff --git a/dart/packages/fory/lib/src/codegen/generated_support.dart b/dart/packages/fory/lib/src/codegen/generated_support.dart
index 838b63c3c0..d1b0f405fc 100644
--- a/dart/packages/fory/lib/src/codegen/generated_support.dart
+++ b/dart/packages/fory/lib/src/codegen/generated_support.dart
@@ -364,7 +364,7 @@ final class GeneratedReadCursor {
 
   int readTaggedUint64() {
     final readIndex = _offset;
-    final first = _view.getInt32(readIndex, Endian.little);
+    final first = _view.getUint32(readIndex, Endian.little);
     if ((first & 1) == 0) {
       _offset = readIndex + 4;
       return first >>> 1;
diff --git a/dart/packages/fory/test/buffer_test.dart b/dart/packages/fory/test/buffer_test.dart
index a371d72325..762b3a9059 100644
--- a/dart/packages/fory/test/buffer_test.dart
+++ b/dart/packages/fory/test/buffer_test.dart
@@ -18,6 +18,7 @@
  */
 
 import 'package:fory/fory.dart';
+import 'package:fory/src/codegen/generated_support.dart';
 import 'package:test/test.dart';
 
 void main() {
@@ -46,5 +47,30 @@ void main() {
       expect(buffer.readVarInt64(), equals(-17));
       expect(buffer.readVarUint64(), equals(9000));
     });
+
+    test('tagged uint64 sign extension regression', () {
+      final buffer = Buffer();
+      final testValue = 0x7FFFFFFF;
+
+      buffer.writeTaggedUint64(testValue);
+      buffer.wrap(buffer.toBytes());
+
+      final result = buffer.readTaggedUint64();
+
+      expect(result, equals(testValue));
+    });
+
+    test('GeneratedReadCursor tagged uint64 sign extension regression', () {
+      final buffer = Buffer();
+      final testValue = 0x7FFFFFFF;
+
+      buffer.writeTaggedUint64(testValue);
+      buffer.wrap(buffer.toBytes());
+
+      final cursor = GeneratedReadCursor.start(buffer);
+      final result = cursor.readTaggedUint64();
+
+      expect(result, equals(testValue));
+    });
   });
 }