diff --git a/core/fxcodec/gif/cfx_gifcontext.cpp b/core/fxcodec/gif/cfx_gifcontext.cpp
index 01babf6..6ce9570 100644
--- a/core/fxcodec/gif/cfx_gifcontext.cpp
+++ b/core/fxcodec/gif/cfx_gifcontext.cpp
@@ -27,10 +27,6 @@
 
 CFX_GifContext::~CFX_GifContext() = default;
 
-uint32_t CFX_GifContext::CurrentPosition() const {
-  return delegate_->GifCurrentPosition();
-}
-
 void CFX_GifContext::ReadScanline(int32_t row_num, uint8_t* row_buf) {
   delegate_->GifReadScanline(row_num, row_buf);
 }
@@ -496,8 +492,7 @@
   }
 
   gif_image->code_exp = code_size;
-  gif_image->data_pos = CurrentPosition();
-  gif_image->data_pos += input_buffer_->GetPosition();
+  gif_image->data_pos = delegate_->GifCurrentPosition();
   gif_image->image_GCE = nullptr;
   if (graphic_control_extension_.get()) {
     if (graphic_control_extension_->gce_flags.transparency) {
diff --git a/core/fxcodec/gif/cfx_gifcontext.h b/core/fxcodec/gif/cfx_gifcontext.h
index 6894da6..2130c8c 100644
--- a/core/fxcodec/gif/cfx_gifcontext.h
+++ b/core/fxcodec/gif/cfx_gifcontext.h
@@ -25,7 +25,6 @@
   explicit CFX_GifContext(GifDecoder::Delegate* delegate);
   ~CFX_GifContext() override;
 
-  uint32_t CurrentPosition() const;
   void ReadScanline(int32_t row_num, uint8_t* row_buf);
   bool GetRecordPosition(uint32_t cur_pos,
                          int32_t left,
diff --git a/core/fxcodec/progressive_decoder.cpp b/core/fxcodec/progressive_decoder.cpp
index 9612025..ad52068 100644
--- a/core/fxcodec/progressive_decoder.cpp
+++ b/core/fxcodec/progressive_decoder.cpp
@@ -371,11 +371,12 @@
                                                    int32_t trans_index,
                                                    bool interlace) {
   m_offSet = rcd_pos;
-  m_InvalidateGifBuffer = true;
 
   FXCODEC_STATUS error_status = FXCODEC_STATUS::kError;
+  m_pCodecMemory->Seek(m_pCodecMemory->GetSize());
   if (!GifReadMoreData(&error_status))
     return false;
+  m_pCodecMemory->Seek(0);
 
   CFX_GifPalette* pPalette = nullptr;
   if (pal_num != 0 && pal_ptr) {
@@ -719,7 +720,7 @@
 bool ProgressiveDecoder::BmpReadMoreData(
     ProgressiveDecoderIface::Context* pContext,
     FXCODEC_STATUS* err_status) {
-  return ReadMoreData(BmpProgressiveDecoder::GetInstance(), pContext, false,
+  return ReadMoreData(BmpProgressiveDecoder::GetInstance(), pContext,
                       err_status);
 }
 
@@ -761,12 +762,8 @@
 
 #ifdef PDF_ENABLE_XFA_GIF
 bool ProgressiveDecoder::GifReadMoreData(FXCODEC_STATUS* err_status) {
-  if (!ReadMoreData(GifProgressiveDecoder::GetInstance(), m_pGifContext.get(),
-                    m_InvalidateGifBuffer, err_status)) {
-    return false;
-  }
-  m_InvalidateGifBuffer = false;
-  return true;
+  return ReadMoreData(GifProgressiveDecoder::GetInstance(), m_pGifContext.get(),
+                      err_status);
 }
 
 bool ProgressiveDecoder::GifDetectImageTypeInBuffer() {
@@ -929,7 +926,7 @@
 
 bool ProgressiveDecoder::JpegReadMoreData(FXCODEC_STATUS* err_status) {
   return ReadMoreData(JpegProgressiveDecoder::GetInstance(),
-                      m_pJpegContext.get(), false, err_status);
+                      m_pJpegContext.get(), err_status);
 }
 
 bool ProgressiveDecoder::JpegDetectImageTypeInBuffer(
@@ -1449,7 +1446,6 @@
 bool ProgressiveDecoder::ReadMoreData(
     ProgressiveDecoderIface* pModule,
     ProgressiveDecoderIface::Context* pContext,
-    bool invalidate_buffer,
     FXCODEC_STATUS* err_status) {
   // Check for EOF.
   if (m_offSet >= static_cast<uint32_t>(m_pFile->GetSize()))
@@ -1460,13 +1456,10 @@
       pdfium::base::checked_cast<uint32_t>(m_pFile->GetSize() - m_offSet);
 
   // Figure out if the codec stopped processing midway through the buffer.
-  size_t dwUnconsumed = 0;
-  if (!invalidate_buffer) {
-    FX_SAFE_SIZE_T avail_input = pModule->GetAvailInput(pContext);
-    if (!avail_input.IsValid())
-      return false;
-    dwUnconsumed = avail_input.ValueOrDie();
-  }
+  size_t dwUnconsumed;
+  FX_SAFE_SIZE_T avail_input = pModule->GetAvailInput(pContext);
+  if (!avail_input.AssignIfValid(&dwUnconsumed))
+    return false;
 
   if (dwUnconsumed == m_pCodecMemory->GetSize()) {
     // Codec couldn't make any progress against the bytes in the buffer.
diff --git a/core/fxcodec/progressive_decoder.h b/core/fxcodec/progressive_decoder.h
index f7bee03..72a5041 100644
--- a/core/fxcodec/progressive_decoder.h
+++ b/core/fxcodec/progressive_decoder.h
@@ -197,7 +197,6 @@
                        CFX_DIBAttribute* pAttribute);
   bool ReadMoreData(ProgressiveDecoderIface* pModule,
                     ProgressiveDecoderIface::Context* pContext,
-                    bool invalidate_buffer,
                     FXCODEC_STATUS* err_status);
 
   int GetDownScale();
@@ -265,7 +264,6 @@
   int32_t m_GifPltNumber = 0;
   int m_GifTransIndex = -1;
   FX_RECT m_GifFrameRect;
-  bool m_InvalidateGifBuffer = true;
 #endif  // PDF_ENABLE_XFA_GIF
 #ifdef PDF_ENABLE_XFA_BMP
   bool m_BmpIsTopBottom = false;
diff --git a/core/fxcodec/progressive_decoder_unittest.cpp b/core/fxcodec/progressive_decoder_unittest.cpp
index 7de25bf..4c1b2c4 100644
--- a/core/fxcodec/progressive_decoder_unittest.cpp
+++ b/core/fxcodec/progressive_decoder_unittest.cpp
@@ -4,9 +4,19 @@
 
 #include "core/fxcodec/progressive_decoder.h"
 
+#include <stddef.h>
+#include <stdint.h>
+
+#include <memory>
+#include <tuple>
+
 #include "core/fxcodec/fx_codec.h"
+#include "core/fxcodec/fx_codec_def.h"
 #include "core/fxcrt/cfx_readonlymemorystream.h"
+#include "core/fxcrt/retain_ptr.h"
 #include "core/fxge/dib/cfx_dibitmap.h"
+#include "core/fxge/dib/fx_dib.h"
+#include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/base/span.h"
 
@@ -16,7 +26,85 @@
 
 namespace fxcodec {
 
+namespace {
+
+using ::testing::ElementsAre;
+
+FXCODEC_STATUS DecodeToBitmap(ProgressiveDecoder& decoder,
+                              const fxcrt::RetainPtr<CFX_DIBitmap>& bitmap) {
+  FXCODEC_STATUS status = decoder.StartDecode(bitmap, 0, 0, bitmap->GetWidth(),
+                                              bitmap->GetHeight());
+  while (status == FXCODEC_STATUS::kDecodeToBeContinued)
+    status = decoder.ContinueDecode();
+  return status;
+}
+
+}  // namespace
+
 #ifdef PDF_ENABLE_XFA_GIF
+TEST(ProgressiveDecoder, Gif87a) {
+  static constexpr uint8_t kInput[] = {
+      0x47, 0x49, 0x46, 0x38, 0x37, 0x61, 0x01, 0x00, 0x01, 0x00, 0x80, 0x01,
+      0x00, 0x40, 0x80, 0xc0, 0x80, 0x80, 0x80, 0x2c, 0x00, 0x00, 0x00, 0x00,
+      0x01, 0x00, 0x01, 0x00, 0x00, 0x02, 0x02, 0x44, 0x01, 0x00, 0x3b};
+
+  auto decoder = std::make_unique<ProgressiveDecoder>();
+
+  auto source = pdfium::MakeRetain<CFX_ReadOnlyMemoryStream>(kInput);
+  CFX_DIBAttribute attr;
+  FXCODEC_STATUS status =
+      decoder->LoadImageInfo(source, FXCODEC_IMAGE_GIF, &attr, true);
+  ASSERT_EQ(FXCODEC_STATUS::kFrameReady, status);
+
+  ASSERT_EQ(1, decoder->GetWidth());
+  ASSERT_EQ(1, decoder->GetHeight());
+
+  auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
+  bitmap->Create(decoder->GetWidth(), decoder->GetHeight(),
+                 FXDIB_Format::kArgb);
+
+  size_t frames;
+  std::tie(status, frames) = decoder->GetFrames();
+  ASSERT_EQ(FXCODEC_STATUS::kDecodeReady, status);
+  ASSERT_EQ(1u, frames);
+
+  status = DecodeToBitmap(*decoder, bitmap);
+  EXPECT_EQ(FXCODEC_STATUS::kDecodeFinished, status);
+  EXPECT_THAT(bitmap->GetScanline(0), ElementsAre(0xc0, 0x80, 0x40, 0xff));
+}
+
+TEST(ProgressiveDecoder, Gif89a) {
+  static constexpr uint8_t kInput[] = {
+      0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00, 0x80,
+      0x01, 0x00, 0x40, 0x80, 0xc0, 0x80, 0x80, 0x80, 0x21, 0xf9, 0x04,
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x2c, 0x00, 0x00, 0x00, 0x00, 0x01,
+      0x00, 0x01, 0x00, 0x00, 0x02, 0x02, 0x44, 0x01, 0x00, 0x3b};
+
+  auto decoder = std::make_unique<ProgressiveDecoder>();
+
+  auto source = pdfium::MakeRetain<CFX_ReadOnlyMemoryStream>(kInput);
+  CFX_DIBAttribute attr;
+  FXCODEC_STATUS status =
+      decoder->LoadImageInfo(source, FXCODEC_IMAGE_GIF, &attr, true);
+  ASSERT_EQ(FXCODEC_STATUS::kFrameReady, status);
+
+  ASSERT_EQ(1, decoder->GetWidth());
+  ASSERT_EQ(1, decoder->GetHeight());
+
+  auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
+  bitmap->Create(decoder->GetWidth(), decoder->GetHeight(),
+                 FXDIB_Format::kArgb);
+
+  size_t frames;
+  std::tie(status, frames) = decoder->GetFrames();
+  ASSERT_EQ(FXCODEC_STATUS::kDecodeReady, status);
+  ASSERT_EQ(1u, frames);
+
+  status = DecodeToBitmap(*decoder, bitmap);
+  EXPECT_EQ(FXCODEC_STATUS::kDecodeFinished, status);
+  EXPECT_THAT(bitmap->GetScanline(0), ElementsAre(0xc0, 0x80, 0x40, 0xff));
+}
+
 TEST(ProgressiveDecoder, BUG_895009) {
   static constexpr uint8_t kInput[] = {
       0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x62, 0x00, 0x21, 0x1b, 0x27, 0x01,
@@ -369,33 +457,28 @@
       0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 
-  {
-    auto decoder = std::make_unique<ProgressiveDecoder>();
+  auto decoder = std::make_unique<ProgressiveDecoder>();
 
-    auto source = pdfium::MakeRetain<CFX_ReadOnlyMemoryStream>(kInput);
-    CFX_DIBAttribute attr;
-    FXCODEC_STATUS status =
-        decoder->LoadImageInfo(source, FXCODEC_IMAGE_GIF, &attr, true);
-    ASSERT_EQ(FXCODEC_STATUS::kFrameReady, status);
+  auto source = pdfium::MakeRetain<CFX_ReadOnlyMemoryStream>(kInput);
+  CFX_DIBAttribute attr;
+  FXCODEC_STATUS status =
+      decoder->LoadImageInfo(source, FXCODEC_IMAGE_GIF, &attr, true);
+  ASSERT_EQ(FXCODEC_STATUS::kFrameReady, status);
 
-    ASSERT_EQ(98, decoder->GetWidth());
-    ASSERT_EQ(6945, decoder->GetHeight());
+  ASSERT_EQ(98, decoder->GetWidth());
+  ASSERT_EQ(6945, decoder->GetHeight());
 
-    auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
-    bitmap->Create(decoder->GetWidth(), decoder->GetHeight(),
-                   FXDIB_Format::kArgb);
+  auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
+  bitmap->Create(decoder->GetWidth(), decoder->GetHeight(),
+                 FXDIB_Format::kArgb);
 
-    size_t frames;
-    std::tie(status, frames) = decoder->GetFrames();
-    ASSERT_EQ(FXCODEC_STATUS::kDecodeReady, status);
-    ASSERT_EQ(1u, frames);
+  size_t frames;
+  std::tie(status, frames) = decoder->GetFrames();
+  ASSERT_EQ(FXCODEC_STATUS::kDecodeReady, status);
+  ASSERT_EQ(1u, frames);
 
-    status = decoder->StartDecode(bitmap, 0, 0, bitmap->GetWidth(),
-                                  bitmap->GetHeight());
-    while (status == FXCODEC_STATUS::kDecodeToBeContinued)
-      status = decoder->ContinueDecode();
-    EXPECT_EQ(FXCODEC_STATUS::kDecodeFinished, status);
-  }
+  status = DecodeToBitmap(*decoder, bitmap);
+  EXPECT_EQ(FXCODEC_STATUS::kDecodeFinished, status);
 }
 #endif  // PDF_ENABLE_XFA_GIF