diff --git a/fpdfsdk/fpdf_attachment.cpp b/fpdfsdk/fpdf_attachment.cpp
index 259ed65..937b504 100644
--- a/fpdfsdk/fpdf_attachment.cpp
+++ b/fpdfsdk/fpdf_attachment.cpp
@@ -131,7 +131,7 @@
 
 FPDF_EXPORT unsigned long FPDF_CALLCONV
 FPDFAttachment_GetName(FPDF_ATTACHMENT attachment,
-                       void* buffer,
+                       FPDF_WCHAR* buffer,
                        unsigned long buflen) {
   CPDF_Object* pFile = CPDFObjectFromFPDFAttachment(attachment);
   if (!pFile)
@@ -186,7 +186,7 @@
 FPDF_EXPORT unsigned long FPDF_CALLCONV
 FPDFAttachment_GetStringValue(FPDF_ATTACHMENT attachment,
                               FPDF_BYTESTRING key,
-                              void* buffer,
+                              FPDF_WCHAR* buffer,
                               unsigned long buflen) {
   CPDF_Object* pFile = CPDFObjectFromFPDFAttachment(attachment);
   if (!pFile)
diff --git a/fpdfsdk/fpdf_attachment_embeddertest.cpp b/fpdfsdk/fpdf_attachment_embeddertest.cpp
index 59508ee..7ce6003 100644
--- a/fpdfsdk/fpdf_attachment_embeddertest.cpp
+++ b/fpdfsdk/fpdf_attachment_embeddertest.cpp
@@ -27,19 +27,18 @@
   ASSERT_TRUE(attachment);
 
   // Check that the name of the first attachment is correct.
-  unsigned long len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  std::vector<char> buf(len);
-  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"1.txt",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  unsigned long length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(12u, length_bytes);
+  std::vector<FPDF_WCHAR> buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"1.txt", GetPlatformWString(buf.data()));
 
   // Check that the content of the first attachment is correct.
-  len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  ASSERT_EQ(4u, FPDFAttachment_GetFile(attachment, buf.data(), len));
-  EXPECT_EQ(std::string("test"), std::string(buf.data(), 4));
+  length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+  std::vector<char> content_buf(length_bytes);
+  ASSERT_EQ(
+      4u, FPDFAttachment_GetFile(attachment, content_buf.data(), length_bytes));
+  EXPECT_EQ(std::string("test"), std::string(content_buf.data(), 4));
 
   // Check that a non-existent key does not exist.
   EXPECT_FALSE(FPDFAttachment_HasKey(attachment, "none"));
@@ -52,40 +51,40 @@
             FPDFAttachment_GetStringValue(attachment, kSizeKey, nullptr, 0));
 
   // Check that the creation date of the first attachment is correct.
-  len = FPDFAttachment_GetStringValue(attachment, kDateKey, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
+  length_bytes =
+      FPDFAttachment_GetStringValue(attachment, kDateKey, nullptr, 0);
+  ASSERT_EQ(48u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
   EXPECT_EQ(48u, FPDFAttachment_GetStringValue(attachment, kDateKey, buf.data(),
-                                               len));
-  EXPECT_STREQ(L"D:20170712214438-07'00'",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+                                               length_bytes));
+  EXPECT_EQ(L"D:20170712214438-07'00'", GetPlatformWString(buf.data()));
 
   // Retrieve the second attachment.
   attachment = FPDFDoc_GetAttachment(document(), 1);
   ASSERT_TRUE(attachment);
 
   // Retrieve the second attachment file.
-  len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  EXPECT_EQ(5869u, FPDFAttachment_GetFile(attachment, buf.data(), len));
+  length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+  content_buf.clear();
+  content_buf.resize(length_bytes);
+  ASSERT_EQ(5869u, FPDFAttachment_GetFile(attachment, content_buf.data(),
+                                          length_bytes));
 
   // Check that the calculated checksum of the file data matches expectation.
   const char kCheckSum[] = "72afcddedf554dda63c0c88e06f1ce18";
   const wchar_t kCheckSumW[] = L"<72AFCDDEDF554DDA63C0C88E06F1CE18>";
-  const std::string generated_checksum =
-      GenerateMD5Base16(reinterpret_cast<uint8_t*>(buf.data()), len);
+  const std::string generated_checksum = GenerateMD5Base16(
+      reinterpret_cast<uint8_t*>(content_buf.data()), length_bytes);
   EXPECT_EQ(kCheckSum, generated_checksum);
 
   // Check that the stored checksum matches expectation.
-  len = FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
+  length_bytes =
+      FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
+  ASSERT_EQ(70u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
   EXPECT_EQ(70u, FPDFAttachment_GetStringValue(attachment, kChecksumKey,
-                                               buf.data(), len));
-  EXPECT_EQ(kCheckSumW,
-            GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data())));
+                                               buf.data(), length_bytes));
+  EXPECT_EQ(kCheckSumW, GetPlatformWString(buf.data()));
 }
 
 TEST_F(FPDFAttachmentEmbedderTest, AddAttachments) {
@@ -112,19 +111,18 @@
   // Verify the name of the new attachment (i.e. the first attachment).
   attachment = FPDFDoc_GetAttachment(document(), 0);
   ASSERT_TRUE(attachment);
-  unsigned long len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  std::vector<char> buf(len);
-  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"0.txt",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  unsigned long length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(12u, length_bytes);
+  std::vector<FPDF_WCHAR> buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"0.txt", GetPlatformWString(buf.data()));
 
   // Verify the content of the new attachment (i.e. the first attachment).
-  len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  ASSERT_EQ(6u, FPDFAttachment_GetFile(attachment, buf.data(), len));
-  EXPECT_EQ(std::string(kContents1), std::string(buf.data(), 6));
+  length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+  std::vector<char> content_buf(length_bytes);
+  ASSERT_EQ(
+      6u, FPDFAttachment_GetFile(attachment, content_buf.data(), length_bytes));
+  EXPECT_EQ(std::string(kContents1), std::string(content_buf.data(), 6));
 
   // Add an attachment to the end of the embedded file list and set its file.
   file_name = GetFPDFWideString(L"z.txt");
@@ -137,20 +135,19 @@
   // Verify the name of the new attachment (i.e. the fourth attachment).
   attachment = FPDFDoc_GetAttachment(document(), 3);
   ASSERT_TRUE(attachment);
-  len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"z.txt",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(12u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"z.txt", GetPlatformWString(buf.data()));
 
   // Verify the content of the new attachment (i.e. the fourth attachment).
-  len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  ASSERT_EQ(6u, FPDFAttachment_GetFile(attachment, buf.data(), len));
-  EXPECT_EQ(std::string(kContents2), std::string(buf.data(), 6));
+  length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+  content_buf.clear();
+  content_buf.resize(length_bytes);
+  ASSERT_EQ(
+      6u, FPDFAttachment_GetFile(attachment, content_buf.data(), length_bytes));
+  EXPECT_EQ(std::string(kContents2), std::string(content_buf.data(), 6));
 }
 
 TEST_F(FPDFAttachmentEmbedderTest, AddAttachmentsWithParams) {
@@ -181,51 +178,49 @@
   // Verify the name of the new attachment (i.e. the second attachment).
   attachment = FPDFDoc_GetAttachment(document(), 1);
   ASSERT_TRUE(attachment);
-  unsigned long len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  std::vector<char> buf(len);
-  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"5.txt",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  unsigned long length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(12u, length_bytes);
+  std::vector<FPDF_WCHAR> buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"5.txt", GetPlatformWString(buf.data()));
 
   // Verify the content of the new attachment.
-  len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  ASSERT_EQ(12u, FPDFAttachment_GetFile(attachment, buf.data(), len));
-  EXPECT_EQ(std::string(kContents), std::string(buf.data(), 12));
+  length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+  std::vector<char> content_buf(length_bytes);
+  ASSERT_EQ(12u, FPDFAttachment_GetFile(attachment, content_buf.data(),
+                                        length_bytes));
+  EXPECT_EQ(std::string(kContents), std::string(content_buf.data(), 12));
 
   // Verify the creation date of the new attachment.
-  len = FPDFAttachment_GetStringValue(attachment, kDateKey, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
+  length_bytes =
+      FPDFAttachment_GetStringValue(attachment, kDateKey, nullptr, 0);
+  ASSERT_EQ(48u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
   EXPECT_EQ(48u, FPDFAttachment_GetStringValue(attachment, kDateKey, buf.data(),
-                                               len));
-  EXPECT_STREQ(kDateW,
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+                                               length_bytes));
+  EXPECT_EQ(kDateW, GetPlatformWString(buf.data()));
 
   // Verify the checksum of the new attachment.
-  len = FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
+  length_bytes =
+      FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
+  ASSERT_EQ(70u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
   EXPECT_EQ(70u, FPDFAttachment_GetStringValue(attachment, kChecksumKey,
-                                               buf.data(), len));
-  EXPECT_STREQ(kCheckSumW,
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+                                               buf.data(), length_bytes));
+  EXPECT_EQ(kCheckSumW, GetPlatformWString(buf.data()));
 
   // Overwrite the existing file with empty content, and check that the checksum
   // gets updated to the correct value.
   EXPECT_TRUE(FPDFAttachment_SetFile(attachment, document(), nullptr, 0));
   EXPECT_EQ(0u, FPDFAttachment_GetFile(attachment, nullptr, 0));
-  len = FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
+  length_bytes =
+      FPDFAttachment_GetStringValue(attachment, kChecksumKey, nullptr, 0);
+  ASSERT_EQ(70u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
   EXPECT_EQ(70u, FPDFAttachment_GetStringValue(attachment, kChecksumKey,
-                                               buf.data(), len));
+                                               buf.data(), length_bytes));
   EXPECT_EQ(L"<D41D8CD98F00B204E9800998ECF8427E>",
-            GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data())));
+            GetPlatformWString(buf.data()));
 }
 
 TEST_F(FPDFAttachmentEmbedderTest, DeleteAttachment) {
@@ -235,12 +230,11 @@
 
   // Verify the name of the first attachment.
   FPDF_ATTACHMENT attachment = FPDFDoc_GetAttachment(document(), 0);
-  unsigned long len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  std::vector<char> buf(len);
-  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"1.txt",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  unsigned long length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(12u, length_bytes);
+  std::vector<FPDF_WCHAR> buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(12u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"1.txt", GetPlatformWString(buf.data()));
 
   // Delete the first attachment.
   EXPECT_TRUE(FPDFDoc_DeleteAttachment(document(), 0));
@@ -248,11 +242,9 @@
 
   // Verify the name of the new first attachment.
   attachment = FPDFDoc_GetAttachment(document(), 0);
-  len = FPDFAttachment_GetName(attachment, nullptr, 0);
-  buf.clear();
-  buf.resize(len);
-  EXPECT_EQ(26u, FPDFAttachment_GetName(attachment, buf.data(), len));
-  EXPECT_STREQ(L"attached.pdf",
-               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
-                   .c_str());
+  length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+  ASSERT_EQ(26u, length_bytes);
+  buf = GetFPDFWideStringBuffer(length_bytes);
+  EXPECT_EQ(26u, FPDFAttachment_GetName(attachment, buf.data(), length_bytes));
+  EXPECT_EQ(L"attached.pdf", GetPlatformWString(buf.data()));
 }
diff --git a/public/fpdf_attachment.h b/public/fpdf_attachment.h
index 7b55974..1c424f6 100644
--- a/public/fpdf_attachment.h
+++ b/public/fpdf_attachment.h
@@ -65,12 +65,12 @@
 //
 //   attachment - handle to an attachment.
 //   buffer     - buffer for holding the file name, encoded in UTF16-LE.
-//   buflen     - length of the buffer.
+//   buflen     - length of the buffer in bytes.
 //
-// Returns the length of the file name.
+// Returns the length of the file name in bytes.
 FPDF_EXPORT unsigned long FPDF_CALLCONV
 FPDFAttachment_GetName(FPDF_ATTACHMENT attachment,
-                       void* buffer,
+                       FPDF_WCHAR* buffer,
                        unsigned long buflen);
 
 // Experimental API.
@@ -122,13 +122,13 @@
 //   attachment - handle to an attachment.
 //   key        - the key to the requested string value, encoded in UTF-8.
 //   buffer     - buffer for holding the string value encoded in UTF16-LE.
-//   buflen     - length of the buffer.
+//   buflen     - length of the buffer in bytes.
 //
-// Returns the length of the dictionary value string.
+// Returns the length of the dictionary value string in bytes.
 FPDF_EXPORT unsigned long FPDF_CALLCONV
 FPDFAttachment_GetStringValue(FPDF_ATTACHMENT attachment,
                               FPDF_BYTESTRING key,
-                              void* buffer,
+                              FPDF_WCHAR* buffer,
                               unsigned long buflen);
 
 // Experimental API.
diff --git a/samples/pdfium_test_write_helper.cc b/samples/pdfium_test_write_helper.cc
index 5b3fe2d..23164a8 100644
--- a/samples/pdfium_test_write_helper.cc
+++ b/samples/pdfium_test_write_helper.cc
@@ -511,15 +511,13 @@
 
     // Retrieve the attachment file name.
     std::string attachment_name;
-    unsigned long len = FPDFAttachment_GetName(attachment, nullptr, 0);
-    if (len) {
-      std::vector<char> buf(len);
-      unsigned long actual_len =
-          FPDFAttachment_GetName(attachment, buf.data(), len);
-      if (actual_len == len) {
-        attachment_name =
-            GetPlatformString(reinterpret_cast<unsigned short*>(buf.data()));
-      }
+    unsigned long length_bytes = FPDFAttachment_GetName(attachment, nullptr, 0);
+    if (length_bytes) {
+      std::vector<FPDF_WCHAR> buf = GetFPDFWideStringBuffer(length_bytes);
+      unsigned long actual_length_bytes =
+          FPDFAttachment_GetName(attachment, buf.data(), length_bytes);
+      if (actual_length_bytes == length_bytes)
+        attachment_name = GetPlatformString(buf.data());
     }
     if (attachment_name.empty()) {
       fprintf(stderr, "Attachment #%d has an empty file name.\n", i + 1);
@@ -538,12 +536,12 @@
     }
 
     // Retrieve the attachment.
-    len = FPDFAttachment_GetFile(attachment, nullptr, 0);
-    std::vector<char> data_buf(len);
-    if (len) {
-      unsigned long actual_len =
-          FPDFAttachment_GetFile(attachment, data_buf.data(), len);
-      if (actual_len != len)
+    length_bytes = FPDFAttachment_GetFile(attachment, nullptr, 0);
+    std::vector<char> data_buf(length_bytes);
+    if (length_bytes) {
+      unsigned long actual_length_bytes =
+          FPDFAttachment_GetFile(attachment, data_buf.data(), length_bytes);
+      if (actual_length_bytes != length_bytes)
         data_buf.clear();
     }
     if (data_buf.empty()) {
@@ -558,8 +556,8 @@
       continue;
     }
 
-    size_t written_len = fwrite(data_buf.data(), 1, len, fp);
-    if (written_len == len) {
+    size_t written_len = fwrite(data_buf.data(), 1, length_bytes, fp);
+    if (written_len == length_bytes) {
       fprintf(stderr, "Saved attachment \"%s\" as: %s.\n",
               attachment_name.c_str(), save_name);
     } else {