diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5f7ab8a7e..a48ffd483 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -351,6 +351,8 @@ if(CMAKE_C_COMPILER_ID STREQUAL "GNU" OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${NEEDED_CXX_COMPILER_FLAGS_STRING}")
 endif()
 
+include(LargeFileSupport)
+
 set(NEEDED_HEADERS
     stdbool.h
     sys/statvfs.h
@@ -377,7 +379,6 @@ set(NEEDED_FUNCTIONS
     htonll
     iconv_open
     localtime_r
-    lseek64
     memmem
     mkdtemp
     ntohll
diff --git a/cmake/LargeFileSupport.cmake b/cmake/LargeFileSupport.cmake
new file mode 100644
index 000000000..01225e708
--- /dev/null
+++ b/cmake/LargeFileSupport.cmake
@@ -0,0 +1,33 @@
+# Based on AC_SYS_LARGEFILE
+
+if(NOT DEFINED NO_LFS_MACROS_REQUIRED)
+    include(CheckCSourceCompiles)
+
+    # Check that off_t can represent 2**63 - 1 correctly.
+    # We can't simply define LARGE_OFF_T to be 9223372036854775807,
+    # since some C++ compilers masquerading as C compilers
+    # incorrectly reject 9223372036854775807.
+    set(LFS_TEST_PROGRAM "
+        #include <sys/types.h>
+        #define LARGE_OFF_T (((off_t) 1 << 62) - 1 + ((off_t) 1 << 62))
+        int off_t_is_large[(LARGE_OFF_T % 2147483629 == 721 && LARGE_OFF_T % 2147483647 == 1) ? 1 : -1];
+        int main() { return 0; }
+    ")
+
+    check_c_source_compiles("${LFS_TEST_PROGRAM}" NO_LFS_MACROS_REQUIRED)
+    if(NOT NO_LFS_MACROS_REQUIRED)
+        if(NOT DEFINED FILE_OFFSET_BITS_LFS_MACRO_REQUIRED)
+            check_c_source_compiles("#define _FILE_OFFSET_BITS 64 ${LFS_TEST_PROGRAM}" FILE_OFFSET_BITS_LFS_MACRO_REQUIRED)
+            if(FILE_OFFSET_BITS_LFS_MACRO_REQUIRED)
+                add_definitions(-D_FILE_OFFSET_BITS=64)
+            elseif(NOT DEFINED LARGE_FILES_LFS_MACRO_REQUIRED)
+                check_c_source_compiles("#define _LARGE_FILES 1 ${LFS_TEST_PROGRAM}" LARGE_FILES_LFS_MACRO_REQUIRED)
+                if(LARGE_FILES_LFS_MACRO_REQUIRED)
+                    add_definitions(-D_LARGE_FILES=1)
+                endif()
+            endif()
+        endif()
+    endif()
+
+    unset(LFS_TEST_PROGRAM)
+endif()
diff --git a/configure.ac b/configure.ac
index 76272089f..a02f7a122 100644
--- a/configure.ac
+++ b/configure.ac
@@ -182,7 +182,6 @@ AC_SUBST(CRYPTO_LIBS)
 
 
 AC_SYS_LARGEFILE
-AC_CHECK_FUNCS([lseek64])
 
 AC_FUNC_GETMNTENT
 
diff --git a/libtransmission/file-posix.c b/libtransmission/file-posix.c
index 2108f84d5..d9469f392 100644
--- a/libtransmission/file-posix.c
+++ b/libtransmission/file-posix.c
@@ -23,10 +23,6 @@
  #define _DARWIN_C_SOURCE
 #endif
 
-#if !defined (_LARGEFILE64_SOURCE)
- #define _LARGEFILE64_SOURCE
-#endif
-
 #include <assert.h>
 #include <dirent.h>
 #include <errno.h>
@@ -68,14 +64,6 @@
  #define PATH_MAX 4096
 #endif
 
-#ifdef HAVE_LSEEK64
- #define tr_off_t off64_t
- #define tr_lseek lseek64
-#else
- #define tr_off_t off_t
- #define tr_lseek lseek
-#endif
-
 /* don't use pread/pwrite on old versions of uClibc because they're buggy.
  * https://trac.transmissionbt.com/ticket/3826 */
 #ifdef __UCLIBC__
@@ -542,7 +530,7 @@ tr_sys_file_seek (tr_sys_file_t       handle,
                   tr_error         ** error)
 {
   bool ret = false;
-  tr_off_t my_new_offset;
+  off_t my_new_offset;
 
   TR_STATIC_ASSERT (TR_SEEK_SET == SEEK_SET, "values should match");
   TR_STATIC_ASSERT (TR_SEEK_CUR == SEEK_CUR, "values should match");
@@ -553,7 +541,7 @@ tr_sys_file_seek (tr_sys_file_t       handle,
   assert (handle != TR_BAD_SYS_FILE);
   assert (origin == TR_SEEK_SET || origin == TR_SEEK_CUR || origin == TR_SEEK_END);
 
-  my_new_offset = tr_lseek (handle, offset, origin);
+  my_new_offset = lseek (handle, offset, origin);
 
   if (my_new_offset != -1)
     {
@@ -624,7 +612,7 @@ tr_sys_file_read_at (tr_sys_file_t    handle,
 
 #else
 
-  if (tr_lseek (handle, offset, SEEK_SET) != -1)
+  if (lseek (handle, offset, SEEK_SET) != -1)
     my_bytes_read = read (handle, buffer, size);
   else
     my_bytes_read = -1;
@@ -700,7 +688,7 @@ tr_sys_file_write_at (tr_sys_file_t    handle,
 
 #else
 
-  if (tr_lseek (handle, offset, SEEK_SET) != -1)
+  if (lseek (handle, offset, SEEK_SET) != -1)
     my_bytes_written = write (handle, buffer, size);
   else
     my_bytes_written = -1;