diff --git a/core/fxge/dib/cfx_dibbase.h b/core/fxge/dib/cfx_dibbase.h
index 905d283..66fd6a8 100644
--- a/core/fxge/dib/cfx_dibbase.h
+++ b/core/fxge/dib/cfx_dibbase.h
@@ -45,6 +45,7 @@
 
   static constexpr uint32_t kPaletteSize = 256;
 
+  // Note that the returned scanline includes unused space at the end, if any.
   virtual pdfium::span<const uint8_t> GetScanline(int line) const = 0;
   virtual bool SkipToScanline(int line, PauseIndicatorIface* pPause) const;
   virtual size_t GetEstimatedImageMemoryBurden() const;
@@ -53,9 +54,12 @@
   virtual RetainPtr<const CFX_DIBitmap> RealizeIfNeeded() const;
 #endif
 
+  // Note that the returned scanline does not include unused space at the end,
+  // if any.
   template <typename T>
   pdfium::span<const T> GetScanlineAs(int line) const {
-    return fxcrt::reinterpret_span<const T>(GetScanline(line));
+    return fxcrt::reinterpret_span<const T>(GetScanline(line))
+        .first(GetWidth());
   }
 
   int GetWidth() const { return width_; }
diff --git a/core/fxge/dib/cfx_dibitmap.h b/core/fxge/dib/cfx_dibitmap.h
index 53e646f..b98ae8f 100644
--- a/core/fxge/dib/cfx_dibitmap.h
+++ b/core/fxge/dib/cfx_dibitmap.h
@@ -70,6 +70,7 @@
         pdfium::make_span(const_cast<uint8_t*>(src.data()), src.size()));
   }
 
+  // Note that the returned scanline includes unused space at the end, if any.
   pdfium::span<uint8_t> GetWritableScanline(int line) {
     pdfium::span<const uint8_t> src = GetScanline(line);
     // SAFETY: const_cast<>() doesn't change size.
@@ -77,9 +78,12 @@
         pdfium::make_span(const_cast<uint8_t*>(src.data()), src.size()));
   }
 
+  // Note that the returned scanline does not include unused space at the end,
+  // if any.
   template <typename T>
   pdfium::span<T> GetWritableScanlineAs(int line) {
-    return fxcrt::reinterpret_span<T>(GetWritableScanline(line));
+    return fxcrt::reinterpret_span<T>(GetWritableScanline(line))
+        .first(GetWidth());
   }
 
   void TakeOver(RetainPtr<CFX_DIBitmap>&& pSrcBitmap);
diff --git a/core/fxge/dib/cfx_dibitmap_unittest.cpp b/core/fxge/dib/cfx_dibitmap_unittest.cpp
index c46110f..e728060 100644
--- a/core/fxge/dib/cfx_dibitmap_unittest.cpp
+++ b/core/fxge/dib/cfx_dibitmap_unittest.cpp
@@ -118,6 +118,22 @@
                                                    FXDIB_Format::k8bppRgb, 0));
 }
 
+TEST(CFXDIBitmapTest, GetScanlineAsWith24Bpp) {
+  auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();
+  ASSERT_TRUE(bitmap->Create(3, 3, FXDIB_Format::kRgb));
+  EXPECT_EQ(3, bitmap->GetWidth());
+  EXPECT_EQ(12u, bitmap->GetPitch());
+
+  EXPECT_EQ(36u, bitmap->GetBuffer().size());
+  EXPECT_EQ(12u, bitmap->GetScanline(0).size());
+  EXPECT_EQ(3u, bitmap->GetScanlineAs<FX_BGR_STRUCT<uint8_t>>(0).size());
+
+  EXPECT_EQ(36u, bitmap->GetWritableBuffer().size());
+  EXPECT_EQ(12u, bitmap->GetWritableScanline(0).size());
+  EXPECT_EQ(3u,
+            bitmap->GetWritableScanlineAs<FX_BGR_STRUCT<uint8_t>>(0).size());
+}
+
 #if defined(PDF_USE_SKIA)
 TEST(CFXDIBitmapTest, UnPreMultiplyFromPreMultiplied) {
   auto bitmap = pdfium::MakeRetain<CFX_DIBitmap>();