diff -ruN gcal-4.1.orig/lib/fseeko.c gcal-4.1/lib/fseeko.c
--- gcal-4.1.orig/lib/fseeko.c	2017-01-22 18:09:38.000000000 +0100
+++ gcal-4.1/lib/fseeko.c	2018-10-27 21:56:46.232442299 +0200
@@ -1,9 +1,9 @@
 /* An fseeko() function that, together with fflush(), is POSIX compliant.
-   Copyright (C) 2007-2017 Free Software Foundation, Inc.
+   Copyright (C) 2007-2018 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
-   the Free Software Foundation; either version 3, or (at your option)
+   the Free Software Foundation; either version 2, or (at your option)
    any later version.
 
    This program is distributed in the hope that it will be useful,
@@ -12,7 +12,7 @@
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License along
-   with this program; if not, see <http://www.gnu.org/licenses/>.  */
+   with this program; if not, see <https://www.gnu.org/licenses/>.  */
 
 #include <config.h>
 
@@ -33,9 +33,9 @@
 #endif
 #if _GL_WINDOWS_64_BIT_OFF_T
 # undef fseeko
-# if HAVE__FSEEKI64 /* msvc, mingw64 */
+# if HAVE__FSEEKI64 && HAVE_DECL__FSEEKI64 /* msvc, mingw since msvcrt8.0, mingw64 */
 #  define fseeko _fseeki64
-# else /* mingw */
+# else /* mingw before msvcrt8.0 */
 #  define fseeko fseeko64
 # endif
 #endif
@@ -47,7 +47,8 @@
 #endif
 
   /* These tests are based on fpurge.c.  */
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
+  /* GNU libc, BeOS, Haiku, Linux libc5 */
   if (fp->_IO_read_end == fp->_IO_read_ptr
       && fp->_IO_write_ptr == fp->_IO_write_base
       && fp->_IO_save_base == NULL)
@@ -80,7 +81,7 @@
 #elif defined __minix               /* Minix */
   if (fp_->_ptr == fp_->_buf
       && (fp_->_ptr == NULL || fp_->_count == 0))
-#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel */
+#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel, OpenVMS */
   if (fp_->_ptr == fp_->_base
       && (fp_->_ptr == NULL || fp_->_cnt == 0))
 #elif defined __UCLIBC__            /* uClibc */
@@ -123,7 +124,8 @@
           return -1;
         }
 
-#if defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1 /* GNU libc, BeOS, Haiku, Linux libc5 */
+#if defined _IO_EOF_SEEN || defined _IO_ftrylockfile || __GNU_LIBRARY__ == 1
+      /* GNU libc, BeOS, Haiku, Linux libc5 */
       fp->_flags &= ~_IO_EOF_SEEN;
       fp->_offset = pos;
 #elif defined __sferror || defined __DragonFly__ || defined __ANDROID__
@@ -150,7 +152,7 @@
       fp_->_flags &= ~__SEOF;
 #elif defined __EMX__               /* emx+gcc */
       fp->_flags &= ~_IOEOF;
-#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel */
+#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, OpenServer, mingw, MSVC, NonStop Kernel, OpenVMS */
       fp_->_flag &= ~_IOEOF;
 #elif defined __MINT__              /* Atari FreeMiNT */
       fp->__offset = pos;