diff --git a/fpdfsdk/fpdf_annot.cpp b/fpdfsdk/fpdf_annot.cpp
index d77cee6..2ef525b 100644
--- a/fpdfsdk/fpdf_annot.cpp
+++ b/fpdfsdk/fpdf_annot.cpp
@@ -14,6 +14,7 @@
 #include "core/fpdfapi/page/cpdf_page.h"
 #include "core/fpdfapi/page/cpdf_pageobject.h"
 #include "core/fpdfapi/parser/cpdf_array.h"
+#include "core/fpdfapi/parser/cpdf_boolean.h"
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
 #include "core/fpdfapi/parser/cpdf_document.h"
 #include "core/fpdfapi/parser/cpdf_name.h"
@@ -217,6 +218,44 @@
   return context ? context->GetAnnotDict() : nullptr;
 }
 
+RetainPtr<CPDF_Dictionary> SetExtGStateInResourceDict(
+    CPDF_Document* pDoc,
+    const CPDF_Dictionary* pAnnotDict,
+    const ByteString& sBlendMode) {
+  auto pGSDict =
+      pdfium::MakeRetain<CPDF_Dictionary>(pAnnotDict->GetByteStringPool());
+
+  // ExtGState represents a graphics state parameter dictionary.
+  pGSDict->SetNewFor<CPDF_Name>("Type", "ExtGState");
+
+  // CA respresents current stroking alpha specifying constant opacity
+  // value that should be used in transparent imaging model.
+  float fOpacity = pAnnotDict->GetNumberFor("CA");
+
+  pGSDict->SetNewFor<CPDF_Number>("CA", fOpacity);
+
+  // ca represents fill color alpha specifying constant opacity
+  // value that should be used in transparent imaging model.
+  pGSDict->SetNewFor<CPDF_Number>("ca", fOpacity);
+
+  // AIS represents alpha source flag specifying whether current alpha
+  // constant shall be interpreted as shape value (true) or opacity value
+  // (false).
+  pGSDict->SetNewFor<CPDF_Boolean>("AIS", false);
+
+  // BM represents Blend Mode
+  pGSDict->SetNewFor<CPDF_Name>("BM", sBlendMode);
+
+  auto pExtGStateDict =
+      pdfium::MakeRetain<CPDF_Dictionary>(pAnnotDict->GetByteStringPool());
+
+  pExtGStateDict->SetFor("GS", pGSDict);
+
+  auto pResourceDict = pDoc->New<CPDF_Dictionary>();
+  pResourceDict->SetFor("ExtGState", pExtGStateDict);
+  return pResourceDict;
+}
+
 }  // namespace
 
 FPDF_EXPORT FPDF_BOOL FPDF_CALLCONV
@@ -794,6 +833,15 @@
     pStreamDict->SetNewFor<CPDF_Name>(pdfium::annotation::kType, "XObject");
     pStreamDict->SetNewFor<CPDF_Name>(pdfium::annotation::kSubtype, "Form");
     pStreamDict->SetRectFor("BBox", rect);
+    // Transparency values are specified in range [0.0f, 1.0f]. We are strictly
+    // checking for value < 1 and not <= 1 so that the output PDF size does not
+    // unnecessarily bloat up by creating a new dictionary in case of solid
+    // color.
+    if (pAnnotDict->KeyExist("CA") && pAnnotDict->GetNumberFor("CA") < 1.0f) {
+      RetainPtr<CPDF_Dictionary> pResourceDict =
+          SetExtGStateInResourceDict(pDoc, pAnnotDict, "Normal");
+      pStreamDict->SetFor("Resources", pResourceDict);
+    }
 
     // Storing reference to indirect object in annotation's AP
     if (!pApDict)
diff --git a/fpdfsdk/fpdf_annot_unittest.cpp b/fpdfsdk/fpdf_annot_unittest.cpp
index 8acae3d..a5f619e 100644
--- a/fpdfsdk/fpdf_annot_unittest.cpp
+++ b/fpdfsdk/fpdf_annot_unittest.cpp
@@ -16,6 +16,17 @@
 #include "testing/fx_string_testhelpers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+namespace {
+
+const wchar_t kStreamData[] =
+    L"/GS gs 0.0 0.0 0.0 RG 4 w 211.8 747.6 m 211.8 744.8 "
+    L"212.6 743.0 214.2 740.8 "
+    L"c 215.4 739.0 216.8 737.1 218.9 736.1 c 220.8 735.1 221.4 733.0 "
+    L"223.7 732.4 c 232.6 729.9 242.0 730.8 251.2 730.8 c 257.5 730.8 "
+    L"263.0 732.9 269.0 734.4 c S";
+
+}  // namespace
+
 class PDFAnnotTest : public testing::Test {
  protected:
   PDFAnnotTest() = default;
@@ -27,14 +38,11 @@
 
 TEST_F(PDFAnnotTest, SetAP) {
   ScopedFPDFDocument doc(FPDF_CreateNewDocument());
+  ASSERT_TRUE(doc);
   ScopedFPDFPage page(FPDFPage_New(doc.get(), 0, 100, 100));
-  const std::wstring kStreamData =
-      L"0.0 0.0 0.0 RG 4 w 211.8 747.6 m 211.8 744.8 "
-      L"212.6 743.0 214.2 740.8 "
-      L"c 215.4 739.0 216.8 737.1 218.9 736.1 c 220.8 735.1 221.4 733.0 "
-      L"223.7 732.4 c 232.6 729.9 242.0 730.8 251.2 730.8 c 257.5 730.8 "
-      L"263.0 732.9 269.0 734.4 c S";
+  ASSERT_TRUE(page);
   ScopedFPDFWideString ap_stream = GetFPDFWideString(kStreamData);
+  ASSERT_TRUE(ap_stream);
 
   ScopedFPDFAnnotation annot(FPDFPage_CreateAnnot(page.get(), FPDF_ANNOT_INK));
   ASSERT_TRUE(annot);
@@ -47,6 +55,9 @@
   const FS_RECTF bounding_rect{206.0f, 753.0f, 339.0f, 709.0f};
   EXPECT_TRUE(FPDFAnnot_SetRect(annot.get(), &bounding_rect));
 
+  ASSERT_TRUE(FPDFAnnot_SetColor(annot.get(), FPDFANNOT_COLORTYPE_Color,
+                                 /*R=*/255, /*G=*/0, /*B=*/0, /*A=*/255));
+
   EXPECT_TRUE(FPDFAnnot_SetAP(annot.get(), FPDF_ANNOT_APPEARANCEMODE_NORMAL,
                               ap_stream.get()));
 
@@ -59,6 +70,9 @@
   ASSERT_TRUE(ap_dict);
   CPDF_Dictionary* stream_dict = ap_dict->GetDictFor("N");
   ASSERT_TRUE(stream_dict);
+  // Check for non-existence of resources dictionary in case of opaque color
+  CPDF_Dictionary* resources_dict = stream_dict->GetDictFor("Resources");
+  ASSERT_FALSE(resources_dict);
   ByteString type = stream_dict->GetStringFor(pdfium::annotation::kType);
   EXPECT_EQ("XObject", type);
   ByteString sub_type = stream_dict->GetStringFor(pdfium::annotation::kSubtype);
@@ -66,7 +80,7 @@
 
   // Check that the appearance stream is same as we just set.
   const uint32_t kStreamDataSize =
-      (kStreamData.size() + 1) * sizeof(FPDF_WCHAR);
+      FX_ArraySize(kStreamData) * sizeof(FPDF_WCHAR);
   unsigned long normal_length_bytes = FPDFAnnot_GetAP(
       annot.get(), FPDF_ANNOT_APPEARANCEMODE_NORMAL, nullptr, 0);
   ASSERT_EQ(kStreamDataSize, normal_length_bytes);
@@ -76,3 +90,48 @@
                             buf.data(), normal_length_bytes));
   EXPECT_EQ(kStreamData, GetPlatformWString(buf.data()));
 }
+
+TEST_F(PDFAnnotTest, SetAPWithOpacity) {
+  ScopedFPDFDocument doc(FPDF_CreateNewDocument());
+  ASSERT_TRUE(doc);
+  ScopedFPDFPage page(FPDFPage_New(doc.get(), 0, 100, 100));
+  ASSERT_TRUE(page);
+  ScopedFPDFWideString ap_stream = GetFPDFWideString(kStreamData);
+  ASSERT_TRUE(ap_stream);
+
+  ScopedFPDFAnnotation annot(FPDFPage_CreateAnnot(page.get(), FPDF_ANNOT_INK));
+  ASSERT_TRUE(annot);
+
+  ASSERT_TRUE(FPDFAnnot_SetColor(annot.get(), FPDFANNOT_COLORTYPE_Color,
+                                 /*R=*/255, /*G=*/0, /*B=*/0, /*A=*/102));
+
+  const FS_RECTF bounding_rect{206.0f, 753.0f, 339.0f, 709.0f};
+  EXPECT_TRUE(FPDFAnnot_SetRect(annot.get(), &bounding_rect));
+
+  EXPECT_TRUE(FPDFAnnot_SetAP(annot.get(), FPDF_ANNOT_APPEARANCEMODE_NORMAL,
+                              ap_stream.get()));
+
+  CPDF_AnnotContext* context = CPDFAnnotContextFromFPDFAnnotation(annot.get());
+  ASSERT_TRUE(context);
+  CPDF_Dictionary* annot_dict = context->GetAnnotDict();
+  ASSERT_TRUE(annot_dict);
+  CPDF_Dictionary* ap_dict = annot_dict->GetDictFor(pdfium::annotation::kAP);
+  ASSERT_TRUE(ap_dict);
+  CPDF_Dictionary* stream_dict = ap_dict->GetDictFor("N");
+  ASSERT_TRUE(stream_dict);
+  CPDF_Dictionary* resources_dict = stream_dict->GetDictFor("Resources");
+  ASSERT_TRUE(stream_dict);
+  CPDF_Dictionary* extGState_dict = resources_dict->GetDictFor("ExtGState");
+  ASSERT_TRUE(extGState_dict);
+  CPDF_Dictionary* gs_dict = extGState_dict->GetDictFor("GS");
+  ASSERT_TRUE(gs_dict);
+  ByteString type = gs_dict->GetStringFor(pdfium::annotation::kType);
+  EXPECT_EQ("ExtGState", type);
+  float opacity = gs_dict->GetNumberFor("CA");
+  // Opacity value of 102 is represented as 0.4f (=104/255) in /CA entry.
+  EXPECT_FLOAT_EQ(0.4f, opacity);
+  ByteString blend_mode = gs_dict->GetStringFor("BM");
+  EXPECT_EQ("Normal", blend_mode);
+  bool alpha_source_flag = gs_dict->GetBooleanFor("AIS", true);
+  EXPECT_FALSE(alpha_source_flag);
+}