diff --git a/core/fxcrt/cfx_seekablestreamproxy.cpp b/core/fxcrt/cfx_seekablestreamproxy.cpp
index 67b304f..6c34b03 100644
--- a/core/fxcrt/cfx_seekablestreamproxy.cpp
+++ b/core/fxcrt/cfx_seekablestreamproxy.cpp
@@ -27,27 +27,21 @@
 
 // Returns {src bytes consumed, dst chars produced}.
 // Invalid sequences are silently not output.
-std::pair<size_t, size_t> UTF8Decode(const char* pSrc,
-                                     size_t srcLen,
-                                     wchar_t* pDst,
-                                     size_t dstLen) {
-  ASSERT(pDst);
-  ASSERT(dstLen > 0);
-
-  if (srcLen < 1)
-    return {0, 0};
+std::pair<size_t, size_t> UTF8Decode(pdfium::span<const uint8_t> pSrc,
+                                     pdfium::span<wchar_t> pDst) {
+  ASSERT(!pDst.empty());
 
   uint32_t dwCode = 0;
   int32_t iPending = 0;
   size_t iSrcNum = 0;
   size_t iDstNum = 0;
-  for (size_t iIndex = 0; iIndex < srcLen && iDstNum < dstLen; ++iIndex) {
+  for (size_t iIndex = 0; iIndex < pSrc.size() && iDstNum < pDst.size();
+       ++iIndex) {
     ++iSrcNum;
-    uint8_t byte = static_cast<uint8_t>(*(pSrc + iIndex));
+    uint8_t byte = pSrc[iIndex];
     if (byte < 0x80) {
       iPending = 0;
-      ++iDstNum;
-      *pDst++ = byte;
+      pDst[iDstNum++] = byte;
     } else if (byte < 0xc0) {
       if (iPending < 1)
         continue;
@@ -55,10 +49,8 @@
       dwCode = dwCode << 6;
       dwCode |= (byte & 0x3f);
       --iPending;
-      if (iPending == 0) {
-        ++iDstNum;
-        *pDst++ = dwCode;
-      }
+      if (iPending == 0)
+        pDst[iDstNum++] = dwCode;
     } else if (byte < 0xe0) {
       iPending = 1;
       dwCode = (byte & 0x1f);
@@ -214,26 +206,21 @@
     if (size > 0)
       UTF16ToWChar(pStr, size);
 #endif
-  } else {
-    FX_FILESIZE pos = GetPosition();
-    size_t iBytes = std::min(size, static_cast<size_t>(GetSize() - pos));
-
-    if (iBytes > 0) {
-      std::vector<uint8_t, FxAllocAllocator<uint8_t>> buf(iBytes);
-
-      size_t iLen = ReadData(buf.data(), iBytes);
-      if (m_wCodePage != FX_CODEPAGE_UTF8)
-        return 0;
-
-      size_t iSrc = 0;
-      std::tie(iSrc, size) =
-          UTF8Decode(reinterpret_cast<const char*>(buf.data()), iLen,
-                     static_cast<wchar_t*>(pStr), size);
-      Seek(From::Current, iSrc - iLen);
-    } else {
-      size = 0;
-    }
+    return size;
   }
 
+  FX_FILESIZE pos = GetPosition();
+  size_t iBytes = std::min(size, static_cast<size_t>(GetSize() - pos));
+  if (iBytes == 0)
+    return 0;
+
+  std::vector<uint8_t, FxAllocAllocator<uint8_t>> buf(iBytes);
+  size_t iLen = ReadData(buf.data(), iBytes);
+  if (m_wCodePage != FX_CODEPAGE_UTF8)
+    return 0;
+
+  size_t iSrc;
+  std::tie(iSrc, size) = UTF8Decode({buf.data(), iLen}, {pStr, size});
+  Seek(From::Current, iSrc - iLen);
   return size;
 }