diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index 7ce2eb0adf0..71c1af5bd27 100755
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -173,6 +173,9 @@ endif()
 if( HAVE_SYS_UIO_H )
   check_symbol_exists(writev sys/uio.h HAVE_WRITEV)
 endif()
+set(CMAKE_REQUIRED_DEFINITIONS "-D_LARGEFILE64_SOURCE")
+check_symbol_exists(lseek64 "sys/types.h;unistd.h" HAVE_LSEEK64)
+set(CMAKE_REQUIRED_DEFINITIONS "")
 check_symbol_exists(mallctl malloc_np.h HAVE_MALLCTL)
 check_symbol_exists(mallinfo malloc.h HAVE_MALLINFO)
 check_symbol_exists(malloc_zone_statistics malloc/malloc.h
diff --git a/include/llvm/Config/config.h.cmake b/include/llvm/Config/config.h.cmake
index 1331c4f4cbd..fe87829c2c2 100644
--- a/include/llvm/Config/config.h.cmake
+++ b/include/llvm/Config/config.h.cmake
@@ -120,6 +120,9 @@
 /* Define to 1 if you have the <link.h> header file. */
 #cmakedefine HAVE_LINK_H ${HAVE_LINK_H}
 
+/* Define to 1 if you have the `lseek64' function. */
+#cmakedefine HAVE_LSEEK64 ${HAVE_LSEEK64}
+
 /* Define to 1 if you have the <mach/mach.h> header file. */
 #cmakedefine HAVE_MACH_MACH_H ${HAVE_MACH_MACH_H}
 
diff --git a/lib/Support/raw_ostream.cpp b/lib/Support/raw_ostream.cpp
index 92c7967cd8f..d073802db93 100644
--- a/lib/Support/raw_ostream.cpp
+++ b/lib/Support/raw_ostream.cpp
@@ -598,7 +598,13 @@ void raw_fd_ostream::close() {
 uint64_t raw_fd_ostream::seek(uint64_t off) {
   assert(SupportsSeeking && "Stream does not support seeking!");
   flush();
+#ifdef LLVM_ON_WIN32
+  pos = ::_lseeki64(FD, off, SEEK_SET);
+#elif defined(HAVE_LSEEK64)
+  pos = ::lseek64(FD, off, SEEK_SET);
+#else
   pos = ::lseek(FD, off, SEEK_SET);
+#endif
   if (pos == (uint64_t)-1)
     error_detected();
   return pos;