diff --git a/python/riegeli/bytes/python_writer.cc b/python/riegeli/bytes/python_writer.cc
index ab3f899d..7aef63a4 100644
--- a/python/riegeli/bytes/python_writer.cc
+++ b/python/riegeli/bytes/python_writer.cc
@@ -144,11 +144,11 @@ bool PythonWriter::WriteInternal(absl::string_view src) {
     }
   }
   do {
+    const size_t length_to_write = UnsignedMin(
+        src.size(),
+        absl::bit_floor(size_t{std::numeric_limits<Py_ssize_t>::max()}));
     size_t length_written;
     {
-      const size_t length_to_write = UnsignedMin(
-          src.size(),
-          absl::bit_floor(size_t{std::numeric_limits<Py_ssize_t>::max()}));
       PythonPtr write_result;
       if (!use_bytes_) {
         // Prefer passing a `memoryview` to avoid copying memory.
@@ -198,7 +198,7 @@ bool PythonWriter::WriteInternal(absl::string_view src) {
         length_written = *length_written_opt;
       }
     }
-    if (ABSL_PREDICT_FALSE(length_written > src.size())) {
+    if (ABSL_PREDICT_FALSE(length_written > length_to_write)) {
       return Fail(absl::InternalError("write() wrote more than requested"));
     }
     move_start_pos(length_written);
diff --git a/riegeli/bytes/cfile_reader.cc b/riegeli/bytes/cfile_reader.cc
index cac70b45..44afb34e 100644
--- a/riegeli/bytes/cfile_reader.cc
+++ b/riegeli/bytes/cfile_reader.cc
@@ -320,7 +320,7 @@ bool CFileReaderBase::ReadInternal(size_t min_length, size_t max_length,
           << "fread() succeeded but read less than requested";
       clearerr(src);
       if (!growing_source_) set_exact_size(limit_pos());
-      return length_read >= min_length;
+      return false;
     }
     if (length_read >= min_length) return true;
     dest += length_read;
diff --git a/riegeli/bytes/fd_reader.cc b/riegeli/bytes/fd_reader.cc
index b7c136ab..ab4716ab 100644
--- a/riegeli/bytes/fd_reader.cc
+++ b/riegeli/bytes/fd_reader.cc
@@ -410,6 +410,7 @@ bool FdReaderBase::ReadInternal(size_t min_length, size_t max_length,
       return FailOperation(has_independent_pos_ ? "pread()" : "read()");
     }
 #else   // _WIN32
+    DWORD length_to_read;
     DWORD length_read;
     if (has_independent_pos_) {
       const HANDLE file_handle = reinterpret_cast<HANDLE>(_get_osfhandle(src));
@@ -417,11 +418,11 @@ bool FdReaderBase::ReadInternal(size_t min_length, size_t max_length,
                              file_handle == reinterpret_cast<HANDLE>(-2))) {
         return FailWindowsOperation("_get_osfhandle()");
       }
-      const DWORD length_to_read = IntCast<DWORD>(UnsignedMin(
+      length_to_read = UnsignedMin(
           max_length,
           Position{std::numeric_limits<fd_internal::Offset>::max()} -
               limit_pos(),
-          absl::bit_floor(std::numeric_limits<DWORD>::max())));
+          absl::bit_floor(std::numeric_limits<DWORD>::max()));
       OVERLAPPED overlapped{};
       overlapped.Offset = IntCast<DWORD>(limit_pos() & 0xffffffff);
       overlapped.OffsetHigh = IntCast<DWORD>(limit_pos() >> 32);
@@ -431,12 +432,13 @@ bool FdReaderBase::ReadInternal(size_t min_length, size_t max_length,
         return FailWindowsOperation("ReadFile()");
       }
     } else {
-      const unsigned length_to_read = UnsignedMin(
+      length_to_read = UnsignedMin(
           max_length,
           Position{std::numeric_limits<fd_internal::Offset>::max()} -
               limit_pos(),
           absl::bit_floor(unsigned{std::numeric_limits<int>::max()}));
-      const int length_read_int = _read(src, dest, length_to_read);
+      const int length_read_int =
+          _read(src, dest, IntCast<unsigned>(length_to_read));
       if (ABSL_PREDICT_FALSE(length_read_int < 0)) {
         return FailOperation("_read()");
       }
@@ -447,7 +449,7 @@ bool FdReaderBase::ReadInternal(size_t min_length, size_t max_length,
       if (!growing_source_) set_exact_size(limit_pos());
       return false;
     }
-    RIEGELI_ASSERT_LE(IntCast<size_t>(length_read), max_length)
+    RIEGELI_ASSERT_LE(UnsignedCast(length_read), length_to_read)
 #ifndef _WIN32
         << (has_independent_pos_ ? "pread()" : "read()")
 #else
diff --git a/riegeli/bytes/fd_writer.cc b/riegeli/bytes/fd_writer.cc
index 9dc32510..709a8e73 100644
--- a/riegeli/bytes/fd_writer.cc
+++ b/riegeli/bytes/fd_writer.cc
@@ -481,6 +481,7 @@ bool FdWriterBase::WriteInternal(absl::string_view src) {
       return FailOperation(has_independent_pos_ ? "pwrite()" : "write()");
     }
 #else   // _WIN32
+    DWORD length_to_write;
     DWORD length_written;
     if (has_independent_pos_) {
       const HANDLE file_handle = reinterpret_cast<HANDLE>(_get_osfhandle(dest));
@@ -488,7 +489,7 @@ bool FdWriterBase::WriteInternal(absl::string_view src) {
                              file_handle == reinterpret_cast<HANDLE>(-2))) {
         return FailWindowsOperation("_get_osfhandle()");
       }
-      const DWORD length_to_write = UnsignedMin(
+      length_to_write = UnsignedMin(
           src.size(), absl::bit_floor(std::numeric_limits<DWORD>::max()));
       OVERLAPPED overlapped{};
       overlapped.Offset = IntCast<DWORD>(start_pos() & 0xffffffff);
@@ -499,10 +500,11 @@ bool FdWriterBase::WriteInternal(absl::string_view src) {
         return FailWindowsOperation("WriteFile()");
       }
     } else {
-      const unsigned length_to_write = UnsignedMin(
+      length_to_write = UnsignedMin(
           src.size(),
           absl::bit_floor(unsigned{std::numeric_limits<int>::max()}));
-      const int length_written_int = _write(dest, src.data(), length_to_write);
+      const int length_written_int =
+          _write(dest, src.data(), IntCast<unsigned>(length_to_write));
       if (ABSL_PREDICT_FALSE(length_written_int < 0)) {
         return FailOperation("_write()");
       }
@@ -516,7 +518,7 @@ bool FdWriterBase::WriteInternal(absl::string_view src) {
         << (has_independent_pos_ ? "WriteFile()" : "_write()")
 #endif
         << " returned 0";
-    RIEGELI_ASSERT_LE(IntCast<size_t>(length_written), src.size())
+    RIEGELI_ASSERT_LE(UnsignedCast(length_written), length_to_write)
 #ifndef _WIN32
         << (has_independent_pos_ ? "pwrite()" : "write()")
 #else
diff --git a/riegeli/bytes/istream_reader.cc b/riegeli/bytes/istream_reader.cc
index 7108ae1d..bd625149 100644
--- a/riegeli/bytes/istream_reader.cc
+++ b/riegeli/bytes/istream_reader.cc
@@ -175,7 +175,7 @@ bool IStreamReaderBase::ReadInternal(size_t min_length, size_t max_length,
       }
       length_read = src.readsome(dest, max_length_to_read);
       RIEGELI_ASSERT_GE(length_read, 0) << "negative istream::readsome()";
-      RIEGELI_ASSERT_LE(IntCast<size_t>(length_read), max_length)
+      RIEGELI_ASSERT_LE(length_read, max_length_to_read)
           << "istream::readsome() read more than requested";
       if (ABSL_PREDICT_TRUE(length_read > 0)) goto fragment_read;
       // `std::istream::peek()` returned non-`eof()` but