diff --git a/CMakeLists.txt b/CMakeLists.txt
index 399071a55..ca87a5359 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -865,7 +865,7 @@ CHECK_FUNCTION_EXISTS(getpagesize	HAVE_GETPAGESIZE)
 CHECK_FUNCTION_EXISTS(sysconf	HAVE_SYSCONF)
 CHECK_FUNCTION_EXISTS(mremap	HAVE_MREMAP)
 CHECK_FUNCTION_EXISTS(getrlimit	HAVE_GETRLIMIT)
-
+CHECK_FUNCTION_EXISTS(_filelengthi64 HAVE_FILE_LENGTH_I64)
 
 #####
 # End system inspection checks.
diff --git a/config.h.in.cmake b/config.h.in.cmake
index a9c795b04..46170554c 100644
--- a/config.h.in.cmake
+++ b/config.h.in.cmake
@@ -197,6 +197,9 @@ are set when opening a binary file on Windows. */
 /* Define to 1 if you have the BaseTsd.h header file. */
 #cmakedefine HAVE_BASETSD_H @HAVE_BASETSD_H@
 
+/* Define if we have filelengthi64. */
+#cmakedefine HAVE_FILE_LENGTH_I64 @HAVE_FILE_LENGTH_I64@
+
 /* The size of `double` as computed by sizeof. */
 #cmakedefine SIZEOF_DOUBLE @SIZEOF_DOUBLE@ 
 /* The size of `float` as computed by sizeof. */
diff --git a/libsrc/posixio.c b/libsrc/posixio.c
index 81f65906f..e0aaf50c9 100644
--- a/libsrc/posixio.c
+++ b/libsrc/posixio.c
@@ -1732,7 +1732,7 @@ ncio_px_filesize(ncio *nciop, off_t *filesizep)
 	/* There is a problem with fstat on Windows based systems
 		which manifests (so far) when Config RELEASE is built. 
 		Use _filelengthi64 isntead. */
-#ifdef _MSC_VER
+#ifdef HAVE_FILE_LENGTH_I64
 
 	__int64 file_len = 0;
 	if( (file_len = _filelengthi64(nciop->fd)) < 0) {