diff --git a/libc/src/__support/File/linux/file.cpp b/libc/src/__support/File/linux/file.cpp
--- a/libc/src/__support/File/linux/file.cpp
+++ b/libc/src/__support/File/linux/file.cpp
@@ -11,6 +11,7 @@
 #include "src/__support/File/file.h"
 
 #include "src/__support/CPP/new.h"
+#include "src/__support/File/linux/lseekImpl.h"
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/errno/libc_errno.h"         // For error macros
 
@@ -40,32 +41,10 @@
 
 ErrorOr<long> linux_file_seek(File *f, long offset, int whence) {
   auto *lf = reinterpret_cast<LinuxFile *>(f);
-  long result;
-#ifdef SYS_lseek
-  int ret =
-      __llvm_libc::syscall_impl<int>(SYS_lseek, lf->get_fd(), offset, whence);
-  result = ret;
-#elif defined(SYS_llseek)
-  int ret = __llvm_libc::syscall_impl<int>(SYS_llseek, lf->get_fd(),
-                                           (long)(((uint64_t)(offset)) >> 32),
-                                           (long)offset, &result, whence);
-  result = ret;
-#elif defined(SYS_llseek)
-  int ret = __llvm_libc::syscall_impl<int>(SYS_llseek, lf->get_fd(),
-                                           (long)(((uint64_t)(offset)) >> 32),
-                                           (long)offset, &result, whence);
-  result = ret;
-#elif defined(SYS__llseek)
-  int ret = __llvm_libc::syscall_impl<int>(
-      SYS__llseek, lf->get_fd(), offset >> 32, offset, &result, whence);
-#else
-#error "lseek, llseek and _llseek syscalls not available."
-#endif
-
-  if (ret < 0)
-    return Error(-ret);
-
-  return result;
+  auto result = internal::lseekimpl(lf->get_fd(), offset, whence);
+  if (!result.has_value())
+    return result.error();
+  return result.value();
 }
 
 int linux_file_close(File *f) {
diff --git a/libc/src/unistd/linux/lseek.cpp b/libc/src/__support/File/linux/lseekImpl.h
copy from libc/src/unistd/linux/lseek.cpp
copy to libc/src/__support/File/linux/lseekImpl.h
--- a/libc/src/unistd/linux/lseek.cpp
+++ b/libc/src/__support/File/linux/lseekImpl.h
@@ -6,41 +6,45 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/unistd/lseek.h"
-#include "src/errno/libc_errno.h"
+#ifndef LLVM_LIBC_SRC_SUPPORT_FILE_LINUX_LSEEKIMPL_H
+#define LLVM_LIBC_SRC_SUPPORT_FILE_LINUX_LSEEKIMPL_H
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/errno/libc_errno.h"
 
-#include <stdint.h>
+#include <stdint.h>      // For uint64_t.
 #include <sys/syscall.h> // For syscall numbers.
-#include <unistd.h>
+#include <unistd.h>      // For off_t.
 
 namespace __llvm_libc {
+namespace internal {
 
-LLVM_LIBC_FUNCTION(off_t, lseek, (int fd, off_t offset, int whence)) {
+LIBC_INLINE ErrorOr<off_t> lseekimpl(int fd, off_t offset, int whence) {
   off_t result;
 #ifdef SYS_lseek
   int ret = __llvm_libc::syscall_impl<int>(SYS_lseek, fd, offset, whence);
   result = ret;
 #elif defined(SYS_llseek) || defined(SYS__llseek)
+  static_assert(sizeof(size_t) == 4, "size_t must be 32 bits.");
 #ifdef SYS_llseek
   constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
 #elif defined(SYS__llseek)
   constexpr long LLSEEK_SYSCALL_NO = SYS__llseek;
 #endif
-  uint64_t offset_64 = static_cast<uint64_t>(offset);
+  off_t offset_64 = offset;
   int ret = __llvm_libc::syscall_impl<int>(
       LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
 #else
 #error "lseek, llseek and _llseek syscalls not available."
 #endif
-
-  if (ret < 0) {
-    libc_errno = -ret;
-    return -1;
-  }
+  if (ret < 0)
+    return Error(-ret);
   return result;
 }
 
+} // namespace internal
 } // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_FILE_LINUX_LSEEKIMPL_H
diff --git a/libc/src/unistd/linux/lseek.cpp b/libc/src/unistd/linux/lseek.cpp
--- a/libc/src/unistd/linux/lseek.cpp
+++ b/libc/src/unistd/linux/lseek.cpp
@@ -9,38 +9,22 @@
 #include "src/unistd/lseek.h"
 #include "src/errno/libc_errno.h"
 
+#include "src/__support/File/linux/lseekImpl.h"
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
 
-#include <stdint.h>
 #include <sys/syscall.h> // For syscall numbers.
-#include <unistd.h>
+#include <unistd.h>      // For off_t.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(off_t, lseek, (int fd, off_t offset, int whence)) {
-  off_t result;
-#ifdef SYS_lseek
-  int ret = __llvm_libc::syscall_impl<int>(SYS_lseek, fd, offset, whence);
-  result = ret;
-#elif defined(SYS_llseek) || defined(SYS__llseek)
-#ifdef SYS_llseek
-  constexpr long LLSEEK_SYSCALL_NO = SYS_llseek;
-#elif defined(SYS__llseek)
-  constexpr long LLSEEK_SYSCALL_NO = SYS__llseek;
-#endif
-  uint64_t offset_64 = static_cast<uint64_t>(offset);
-  int ret = __llvm_libc::syscall_impl<int>(
-      LLSEEK_SYSCALL_NO, fd, offset_64 >> 32, offset_64, &result, whence);
-#else
-#error "lseek, llseek and _llseek syscalls not available."
-#endif
-
-  if (ret < 0) {
-    libc_errno = -ret;
+  auto result = internal::lseekimpl(fd, offset, whence);
+  if (!result.has_value()) {
+    libc_errno = result.error();
     return -1;
   }
-  return result;
+  return result.value();
 }
 
 } // namespace __llvm_libc