diff --git a/compat/win/sys/types.h b/compat/win/sys/types.h
index 31797321..5355bcf7 100644
--- a/compat/win/sys/types.h
+++ b/compat/win/sys/types.h
@@ -24,12 +24,6 @@
 
 #include <stdint.h>
 
-#ifdef _WIN64
-typedef int64_t ssize_t;
-#else
-typedef __w64 int ssize_t;
-#endif
-
 typedef unsigned int pid_t;
 
 #endif  // CRASHPAD_COMPAT_WIN_SYS_TYPES_H_
diff --git a/tools/crashpad_database_util.cc b/tools/crashpad_database_util.cc
index e09f1ded..433b4769 100644
--- a/tools/crashpad_database_util.cc
+++ b/tools/crashpad_database_util.cc
@@ -566,7 +566,7 @@ int DatabaseUtilMain(int argc, char* argv[]) {
         call_error_writing_crash_report(database.get(), new_report);
 
     char buf[4096];
-    ssize_t read_result;
+    FileOperationResult read_result;
     do {
       read_result = file_reader->Read(buf, sizeof(buf));
       if (read_result < 0) {
diff --git a/util/file/file_io.cc b/util/file/file_io.cc
index 6f2d0b58..98eb3404 100644
--- a/util/file/file_io.cc
+++ b/util/file/file_io.cc
@@ -20,8 +20,8 @@
 namespace crashpad {
 
 bool LoggingReadFile(FileHandle file, void* buffer, size_t size) {
-  ssize_t expect = base::checked_cast<ssize_t>(size);
-  ssize_t rv = ReadFile(file, buffer, size);
+  FileOperationResult expect = base::checked_cast<FileOperationResult>(size);
+  FileOperationResult rv = ReadFile(file, buffer, size);
   if (rv < 0) {
     PLOG(ERROR) << "read";
     return false;
@@ -35,8 +35,8 @@ bool LoggingReadFile(FileHandle file, void* buffer, size_t size) {
 }
 
 bool LoggingWriteFile(FileHandle file, const void* buffer, size_t size) {
-  ssize_t expect = base::checked_cast<ssize_t>(size);
-  ssize_t rv = WriteFile(file, buffer, size);
+  FileOperationResult expect = base::checked_cast<FileOperationResult>(size);
+  FileOperationResult rv = WriteFile(file, buffer, size);
   if (rv < 0) {
     PLOG(ERROR) << "write";
     return false;
@@ -59,7 +59,7 @@ void CheckedWriteFile(FileHandle file, const void* buffer, size_t size) {
 
 void CheckedReadFileAtEOF(FileHandle file) {
   char c;
-  ssize_t rv = ReadFile(file, &c, 1);
+  FileOperationResult rv = ReadFile(file, &c, 1);
   if (rv < 0) {
     PCHECK(rv == 0) << "read";
   } else {
diff --git a/util/file/file_reader.cc b/util/file/file_reader.cc
index aad55cf7..14d06c74 100644
--- a/util/file/file_reader.cc
+++ b/util/file/file_reader.cc
@@ -21,8 +21,8 @@
 namespace crashpad {
 
 bool FileReaderInterface::ReadExactly(void* data, size_t size) {
-  ssize_t expect = base::checked_cast<ssize_t>(size);
-  ssize_t rv = Read(data, size);
+  FileOperationResult expect = base::checked_cast<FileOperationResult>(size);
+  FileOperationResult rv = Read(data, size);
   if (rv < 0) {
     // Read() will have logged its own error.
     return false;
@@ -41,14 +41,14 @@ WeakFileHandleFileReader::WeakFileHandleFileReader(FileHandle file_handle)
 WeakFileHandleFileReader::~WeakFileHandleFileReader() {
 }
 
-ssize_t WeakFileHandleFileReader::Read(void* data, size_t size) {
+FileOperationResult WeakFileHandleFileReader::Read(void* data, size_t size) {
   DCHECK_NE(file_handle_, kInvalidFileHandle);
 
   // Don’t use LoggingReadFile(), which insists on a full read and only returns
   // a bool. This method permits short reads and returns the number of bytes
   // read.
-  base::checked_cast<ssize_t>(size);
-  ssize_t rv = ReadFile(file_handle_, data, size);
+  base::checked_cast<FileOperationResult>(size);
+  FileOperationResult rv = ReadFile(file_handle_, data, size);
   if (rv < 0) {
     PLOG(ERROR) << "read";
     return -1;
@@ -88,7 +88,7 @@ void FileReader::Close() {
   file_.reset();
 }
 
-ssize_t FileReader::Read(void* data, size_t size) {
+FileOperationResult FileReader::Read(void* data, size_t size) {
   DCHECK(file_.is_valid());
   return weak_file_handle_file_reader_.Read(data, size);
 }
@@ -105,7 +105,7 @@ WeakStdioFileReader::WeakStdioFileReader(FILE* file)
 WeakStdioFileReader::~WeakStdioFileReader() {
 }
 
-ssize_t WeakStdioFileReader::Read(void* data, size_t size) {
+FileOperationResult WeakStdioFileReader::Read(void* data, size_t size) {
   DCHECK(file_);
 
   size_t rv = fread(data, 1, size, file_);
diff --git a/util/file/file_reader.h b/util/file/file_reader.h
index 58f58651..5d77b875 100644
--- a/util/file/file_reader.h
+++ b/util/file/file_reader.h
@@ -37,7 +37,7 @@ class FileReaderInterface : public virtual FileSeekerInterface {
   //! \return The number of bytes actually read if the operation succeeded,
   //!     which may be `0` or any positive value less than or equal to \a size.
   //!     `-1` if the operation failed, with an error message logged.
-  virtual ssize_t Read(void* data, size_t size) = 0;
+  virtual FileOperationResult Read(void* data, size_t size) = 0;
 
   //! \brief Wraps Read(), ensuring that the read succeeded and exactly \a size
   //!     bytes were read.
@@ -69,7 +69,7 @@ class WeakFileHandleFileReader : public FileReaderInterface {
   ~WeakFileHandleFileReader() override;
 
   // FileReaderInterface:
-  ssize_t Read(void* data, size_t size) override;
+  FileOperationResult Read(void* data, size_t size) override;
 
   // FileSeekerInterface:
 
@@ -125,7 +125,7 @@ class FileReader : public FileReaderInterface {
   //!
   //! \note It is only valid to call this method between a successful Open() and
   //!     a Close().
-  ssize_t Read(void* data, size_t size) override;
+  FileOperationResult Read(void* data, size_t size) override;
 
   // FileSeekerInterface:
 
@@ -160,7 +160,7 @@ class WeakStdioFileReader : public FileReaderInterface {
   ~WeakStdioFileReader() override;
 
   // FileReaderInterface:
-  ssize_t Read(void* data, size_t size) override;
+  FileOperationResult Read(void* data, size_t size) override;
 
   // FileSeekerInterface:
 
diff --git a/util/file/string_file.cc b/util/file/string_file.cc
index 061b275b..1c74b3f0 100644
--- a/util/file/string_file.cc
+++ b/util/file/string_file.cc
@@ -33,8 +33,9 @@ StringFile::~StringFile() {
 }
 
 void StringFile::SetString(const std::string& string) {
-  CHECK_LE(string.size(),
-           implicit_cast<size_t>(std::numeric_limits<ssize_t>::max()));
+  CHECK_LE(
+      string.size(),
+      implicit_cast<size_t>(std::numeric_limits<FileOperationResult>::max()));
   string_ = string;
   offset_ = 0;
 }
@@ -44,7 +45,7 @@ void StringFile::Reset() {
   offset_ = 0;
 }
 
-ssize_t StringFile::Read(void* data, size_t size) {
+FileOperationResult StringFile::Read(void* data, size_t size) {
   DCHECK(offset_.IsValid());
 
   const size_t offset = offset_.ValueOrDie();
@@ -54,7 +55,7 @@ ssize_t StringFile::Read(void* data, size_t size) {
 
   const size_t nread = std::min(size, string_.size() - offset);
 
-  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  base::CheckedNumeric<FileOperationResult> new_offset = offset_;
   new_offset += nread;
   if (!new_offset.IsValid()) {
     LOG(ERROR) << "Read(): file too large";
@@ -75,7 +76,7 @@ bool StringFile::Write(const void* data, size_t size) {
     string_.resize(offset);
   }
 
-  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  base::CheckedNumeric<FileOperationResult> new_offset = offset_;
   new_offset += size;
   if (!new_offset.IsValid()) {
     LOG(ERROR) << "Write(): file too large";
@@ -97,7 +98,7 @@ bool StringFile::WriteIoVec(std::vector<WritableIoVec>* iovecs) {
   }
 
   // Avoid writing anything at all if it would cause an overflow.
-  base::CheckedNumeric<ssize_t> new_offset = offset_;
+  base::CheckedNumeric<FileOperationResult> new_offset = offset_;
   for (const WritableIoVec& iov : *iovecs) {
     new_offset += iov.iov_len;
     if (!new_offset.IsValid()) {
diff --git a/util/file/string_file.h b/util/file/string_file.h
index c2e18ada..05f57072 100644
--- a/util/file/string_file.h
+++ b/util/file/string_file.h
@@ -21,6 +21,7 @@
 
 #include "base/basictypes.h"
 #include "base/numerics/safe_math.h"
+#include "util/file/file_io.h"
 #include "util/file/file_reader.h"
 #include "util/file/file_writer.h"
 
@@ -50,7 +51,7 @@ class StringFile : public FileReaderInterface, public FileWriterInterface {
   void Reset();
 
   // FileReaderInterface:
-  ssize_t Read(void* data, size_t size) override;
+  FileOperationResult Read(void* data, size_t size) override;
 
   // FileWriterInterface:
   bool Write(const void* data, size_t size) override;
diff --git a/util/file/string_file_test.cc b/util/file/string_file_test.cc
index e2a8214b..0990daf0 100644
--- a/util/file/string_file_test.cc
+++ b/util/file/string_file_test.cc
@@ -197,13 +197,16 @@ TEST(StringFile, WriteInvalid) {
   EXPECT_EQ(0, string_file.Seek(0, SEEK_CUR));
 
   EXPECT_FALSE(string_file.Write(
-      "", implicit_cast<size_t>(std::numeric_limits<ssize_t>::max()) + 1));
+      "",
+      implicit_cast<size_t>(std::numeric_limits<FileOperationResult>::max()) +
+          1));
   EXPECT_TRUE(string_file.string().empty());
   EXPECT_EQ(0, string_file.Seek(0, SEEK_CUR));
 
   EXPECT_TRUE(string_file.Write("a", 1));
   EXPECT_FALSE(string_file.Write(
-      "", implicit_cast<size_t>(std::numeric_limits<ssize_t>::max())));
+      "",
+      implicit_cast<size_t>(std::numeric_limits<FileOperationResult>::max())));
   EXPECT_EQ(1u, string_file.string().size());
   EXPECT_EQ("a", string_file.string());
   EXPECT_EQ(1, string_file.Seek(0, SEEK_CUR));
@@ -290,7 +293,7 @@ TEST(StringFile, WriteIoVecInvalid) {
   WritableIoVec iov;
   EXPECT_EQ(1, string_file.Seek(1, SEEK_CUR));
   iov.iov_base = "a";
-  iov.iov_len = std::numeric_limits<ssize_t>::max();
+  iov.iov_len = std::numeric_limits<FileOperationResult>::max();
   iovecs.push_back(iov);
   EXPECT_FALSE(string_file.WriteIoVec(&iovecs));
   EXPECT_TRUE(string_file.string().empty());
@@ -300,7 +303,7 @@ TEST(StringFile, WriteIoVecInvalid) {
   iov.iov_base = "a";
   iov.iov_len = 1;
   iovecs.push_back(iov);
-  iov.iov_len = std::numeric_limits<ssize_t>::max() - 1;
+  iov.iov_len = std::numeric_limits<FileOperationResult>::max() - 1;
   iovecs.push_back(iov);
   EXPECT_FALSE(string_file.WriteIoVec(&iovecs));
   EXPECT_TRUE(string_file.string().empty());
@@ -449,7 +452,9 @@ TEST(StringFile, SeekInvalid) {
   EXPECT_EQ(1, string_file.Seek(0, SEEK_CUR));
   EXPECT_LT(string_file.Seek(-1, SEEK_SET), 0);
   EXPECT_EQ(1, string_file.Seek(0, SEEK_CUR));
-  EXPECT_LT(string_file.Seek(std::numeric_limits<ssize_t>::min(), SEEK_SET), 0);
+  EXPECT_LT(string_file.Seek(std::numeric_limits<FileOperationResult>::min(),
+                             SEEK_SET),
+            0);
   EXPECT_EQ(1, string_file.Seek(0, SEEK_CUR));
   EXPECT_LT(string_file.Seek(std::numeric_limits<FileOffset>::min(), SEEK_SET),
             0);
@@ -487,7 +492,8 @@ TEST(StringFile, SeekSet) {
   EXPECT_EQ(10, string_file.Seek(0, SEEK_CUR));
   EXPECT_FALSE(string_file.SeekSet(-1));
   EXPECT_EQ(10, string_file.Seek(0, SEEK_CUR));
-  EXPECT_FALSE(string_file.SeekSet(std::numeric_limits<ssize_t>::min()));
+  EXPECT_FALSE(
+      string_file.SeekSet(std::numeric_limits<FileOperationResult>::min()));
   EXPECT_EQ(10, string_file.Seek(0, SEEK_CUR));
   EXPECT_FALSE(string_file.SeekSet(std::numeric_limits<FileOffset>::min()));
   EXPECT_EQ(10, string_file.Seek(0, SEEK_CUR));
diff --git a/util/net/http_body.cc b/util/net/http_body.cc
index 00acead8..6bc6ec9e 100644
--- a/util/net/http_body.cc
+++ b/util/net/http_body.cc
@@ -32,15 +32,16 @@ StringHTTPBodyStream::StringHTTPBodyStream(const std::string& string)
 StringHTTPBodyStream::~StringHTTPBodyStream() {
 }
 
-ssize_t StringHTTPBodyStream::GetBytesBuffer(uint8_t* buffer, size_t max_len) {
+FileOperationResult StringHTTPBodyStream::GetBytesBuffer(uint8_t* buffer,
+                                                         size_t max_len) {
   size_t num_bytes_remaining = string_.length() - bytes_read_;
   if (num_bytes_remaining == 0) {
     return num_bytes_remaining;
   }
 
-  size_t num_bytes_returned =
-      std::min(std::min(num_bytes_remaining, max_len),
-               implicit_cast<size_t>(std::numeric_limits<ssize_t>::max()));
+  size_t num_bytes_returned = std::min(
+      std::min(num_bytes_remaining, max_len),
+      implicit_cast<size_t>(std::numeric_limits<FileOperationResult>::max()));
   memcpy(buffer, &string_[bytes_read_], num_bytes_returned);
   bytes_read_ += num_bytes_returned;
   return num_bytes_returned;
@@ -53,7 +54,8 @@ FileHTTPBodyStream::FileHTTPBodyStream(const base::FilePath& path)
 FileHTTPBodyStream::~FileHTTPBodyStream() {
 }
 
-ssize_t FileHTTPBodyStream::GetBytesBuffer(uint8_t* buffer, size_t max_len) {
+FileOperationResult FileHTTPBodyStream::GetBytesBuffer(uint8_t* buffer,
+                                                       size_t max_len) {
   switch (file_state_) {
     case kUnopenedFile:
       file_.reset(LoggingOpenFileForRead(path_));
@@ -71,7 +73,7 @@ ssize_t FileHTTPBodyStream::GetBytesBuffer(uint8_t* buffer, size_t max_len) {
       break;
   }
 
-  ssize_t rv = ReadFile(file_.get(), buffer, max_len);
+  FileOperationResult rv = ReadFile(file_.get(), buffer, max_len);
   if (rv == 0) {
     file_.reset();
     file_state_ = kClosedAtEOF;
@@ -90,14 +92,16 @@ CompositeHTTPBodyStream::~CompositeHTTPBodyStream() {
   STLDeleteContainerPointers(parts_.begin(), parts_.end());
 }
 
-ssize_t CompositeHTTPBodyStream::GetBytesBuffer(uint8_t* buffer,
-                                                size_t buffer_len) {
-  ssize_t max_len = std::min(
-      buffer_len, implicit_cast<size_t>(std::numeric_limits<ssize_t>::max()));
-  ssize_t bytes_copied = 0;
+FileOperationResult CompositeHTTPBodyStream::GetBytesBuffer(uint8_t* buffer,
+                                                            size_t buffer_len) {
+  FileOperationResult max_len = std::min(
+      buffer_len,
+      implicit_cast<size_t>(std::numeric_limits<FileOperationResult>::max()));
+  FileOperationResult bytes_copied = 0;
   while (bytes_copied < max_len && current_part_ != parts_.end()) {
-    ssize_t this_read = (*current_part_)->GetBytesBuffer(
-        buffer + bytes_copied, max_len - bytes_copied);
+    FileOperationResult this_read =
+        (*current_part_)
+            ->GetBytesBuffer(buffer + bytes_copied, max_len - bytes_copied);
 
     if (this_read == 0) {
       // If the current part has returned 0 indicating EOF, advance the current
diff --git a/util/net/http_body.h b/util/net/http_body.h
index 3cc2f19d..1646591e 100644
--- a/util/net/http_body.h
+++ b/util/net/http_body.h
@@ -42,7 +42,8 @@ class HTTPBodyStream {
   //! \return On success, a positive number indicating the number of bytes
   //!     actually copied to \a buffer. On failure, a negative number. When
   //!     the stream has no more data, returns `0`.
-  virtual ssize_t GetBytesBuffer(uint8_t* buffer, size_t max_len) = 0;
+  virtual FileOperationResult GetBytesBuffer(uint8_t* buffer,
+                                             size_t max_len) = 0;
 
  protected:
   HTTPBodyStream() {}
@@ -60,7 +61,7 @@ class StringHTTPBodyStream : public HTTPBodyStream {
   ~StringHTTPBodyStream() override;
 
   // HTTPBodyStream:
-  ssize_t GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
+  FileOperationResult GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
 
  private:
   std::string string_;
@@ -81,7 +82,7 @@ class FileHTTPBodyStream : public HTTPBodyStream {
   ~FileHTTPBodyStream() override;
 
   // HTTPBodyStream:
-  ssize_t GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
+  FileOperationResult GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
 
  private:
   enum FileState {
@@ -115,7 +116,7 @@ class CompositeHTTPBodyStream : public HTTPBodyStream {
   ~CompositeHTTPBodyStream() override;
 
   // HTTPBodyStream:
-  ssize_t GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
+  FileOperationResult GetBytesBuffer(uint8_t* buffer, size_t max_len) override;
 
  private:
   PartsList parts_;
diff --git a/util/net/http_body_test.cc b/util/net/http_body_test.cc
index 8ec334d3..ea4d8693 100644
--- a/util/net/http_body_test.cc
+++ b/util/net/http_body_test.cc
@@ -47,7 +47,7 @@ TEST(StringHTTPBodyStream, SmallString) {
 
   std::string string("Hello, world");
   StringHTTPBodyStream stream(string);
-  EXPECT_EQ(implicit_cast<ssize_t>(string.length()),
+  EXPECT_EQ(implicit_cast<FileOperationResult>(string.length()),
             stream.GetBytesBuffer(buf, sizeof(buf)));
 
   std::string actual(reinterpret_cast<const char*>(buf), string.length());
diff --git a/util/net/http_body_test_util.cc b/util/net/http_body_test_util.cc
index 3d732311..c3dbd19c 100644
--- a/util/net/http_body_test_util.cc
+++ b/util/net/http_body_test_util.cc
@@ -18,6 +18,7 @@
 
 #include "base/memory/scoped_ptr.h"
 #include "gtest/gtest.h"
+#include "util/file/file_io.h"
 #include "util/net/http_body.h"
 
 namespace crashpad {
@@ -31,7 +32,7 @@ std::string ReadStreamToString(HTTPBodyStream* stream, size_t buffer_size) {
   scoped_ptr<uint8_t[]> buf(new uint8_t[buffer_size]);
   std::string result;
 
-  ssize_t bytes_read;
+  FileOperationResult bytes_read;
   while ((bytes_read = stream->GetBytesBuffer(buf.get(), buffer_size)) != 0) {
     if (bytes_read < 0) {
       ADD_FAILURE() << "Failed to read from stream: " << bytes_read;
diff --git a/util/net/http_transport_mac.mm b/util/net/http_transport_mac.mm
index 971a9986..aad505d5 100644
--- a/util/net/http_transport_mac.mm
+++ b/util/net/http_transport_mac.mm
@@ -22,6 +22,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/sys_string_conversions.h"
 #include "third_party/apple_cf/CFStreamAbstract.h"
+#include "util/file/file_io.h"
 #include "util/misc/implicit_cast.h"
 #include "util/net/http_body.h"
 
@@ -93,7 +94,8 @@ class HTTPBodyStreamCFReadStream {
       return 0;
     }
 
-    ssize_t bytes_read = GetStream(info)->GetBytesBuffer(buffer, buffer_length);
+    FileOperationResult bytes_read =
+        GetStream(info)->GetBytesBuffer(buffer, buffer_length);
     if (bytes_read < 0) {
       error->error = -1;
       error->domain = kCFStreamErrorDomainCustom;
diff --git a/util/net/http_transport_test.cc b/util/net/http_transport_test.cc
index 0bb29857..fe409998 100644
--- a/util/net/http_transport_test.cc
+++ b/util/net/http_transport_test.cc
@@ -121,7 +121,7 @@ class HTTPTransportTestFixture : public MultiprocessExec {
     // Read until the child's stdout closes.
     std::string request;
     char buf[32];
-    ssize_t bytes_read;
+    FileOperationResult bytes_read;
     while ((bytes_read = ReadFile(ReadPipeHandle(), buf, sizeof(buf))) != 0) {
       ASSERT_GE(bytes_read, 0);
       request.append(buf, bytes_read);
diff --git a/util/net/http_transport_win.cc b/util/net/http_transport_win.cc
index e053311d..9c3d00fe 100644
--- a/util/net/http_transport_win.cc
+++ b/util/net/http_transport_win.cc
@@ -22,8 +22,9 @@
 #include "base/scoped_generic.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
-#include "util/net/http_body.h"
 #include "package.h"
+#include "util/file/file_io.h"
+#include "util/net/http_body.h"
 
 namespace crashpad {
 
@@ -174,7 +175,7 @@ bool HTTPTransportWin::ExecuteSynchronously(std::string* response_body) {
   const size_t kBufferSize = 4096;
   for (;;) {
     uint8_t buffer[kBufferSize];
-    ssize_t bytes_to_write =
+    FileOperationResult bytes_to_write =
         body_stream()->GetBytesBuffer(buffer, sizeof(buffer));
     if (bytes_to_write == 0)
       break;